Is there a parallel to defenestration -- for buses?

You could generally subvehiculate someone, maybe? (Subvehiculation would be the obvious noun then).

In reference to this question, you could even say the person that was handled in such a way was subvehiculate, as an adjective; of course with a schwa in the final syllable).

Since nothing in the dictionary quite fits, we can cut and paste to build

Subusticate:

VERB

to sacrifice an innocent subordinate to the the crushing condemnation and wrath of the larger community for the sake of maintaining the boss's pristine self-asserted innocence:

The explicit word picture of the root bus hides behind the t , a dental accommodation for the generic -ic suffix:

adjective suffix, "having to do with, having the nature of, being, made of, caused by, similar to" (in chemistry, indicating a higher valence than names in -ous),

from French -ique and directly from Latin -icus, which in many cases represents Greek -ikos "in the manner of; pertaining to."

From PIE *-(i)ko, which also yielded Slavic -isku, adjectival suffix indicating origin, the source of the -sky (Russian -skii) in many surnames.

Bustic: having to do with both the bus and getting busted, because the boss can never be busted, and you are close enough to the door to fall out without any pushing that would be obvious from outside the bus.

A bustic atmosphere filled the boardroom when the scandal was revealed.

The prefix sub- is slightly obfuscated by the assimilation of the final b:

word-forming element meaning "under, beneath; behind; from under; resulting from further division,"

from Latin preposition sub "under, below, beneath, at the foot of," also "close to, up to, towards;" of time, "within, during;" figuratively "subject to, in the power of;" also "a little, somewhat" (as in sub-horridus "somewhat rough").

This is said to be from PIE *(s)up- (perhaps representing *ex-upo-), a variant form of the root *upo- "from below," hence "turning upward, upward, up, up from under, over, beyond" (cognates: Sanskrit upa "near, under, up to, on," Greek hypo "under," Gothic iup, Old Norse, Old English upp "up, upward," Hittite up-zi "rises"). The Latin word also was used as a prefix and in various combinations.

In Latin assimilated to following -c-, -f-, -g-, -p-, and often -r- and -m-. In Old French the prefix appears in the full Latin form only "in learned adoptions of old Latin compounds" [OED], and in popular use it was represented by sous-, sou-; as in French souvenir from Latin subvenire, souscrire (Old French souzescrire) from subscribere, etc.

The original meaning is now obscured in many words from Latin (suggest, suspect, subject, etc.). The prefix is active in Modern English, sometimes meaning "subordinate" (as in subcontractor); "inferior" (17c., as in subhuman); "smaller" (18c.); "a part or division of" (c.1800, as in subcontinent).

Subustic: Pertaining throwing you under our bus when we bust you, because you are under us, and nobody under you is big enough for spectators to consider a worthy sacrifice.

John felt his chest restrict with subustic dread.

All our actions will remain obscured by plausible deniability, but something has to happen, hence the suffix -ate:

SUFFIX

Forming verbs such as defenestrate, subusticate.

Never doubt they will subusticate someone before culpability can reach the top.

Other derivatives:

Subusticate (n): the quasi-willing sacrifice: Who saw the logic of assigning Judy as subusticate for Sam's crime?

Subusticant (n): the loyal employee announcing the verdict publicly: Top brass appointed Harry as subusticant for the press conference.

Subusticade (n): the crowd of loyal employees surrounding the subusticant to help throw the victim gracefully under the bus: Ted's subusticade was so big we assumed they were covering up for the President himself.

Subustication (n): the act of throwing another loyal employee under the bus: Subustication was suddenly the third most common cause of termination at Greyhound.

The French word dérouler means to unroll or to make flat. That certainly can happen to someone that ends up under a bus. So, maybe derolate

Thinking of falling under a chariot's wheels (carrum in Latin, giving us car, cart and carriage) might suggest something simple like decarate, which is not very decorous, but is quite decarrous, and you may want to avert your eyes.

As the origin of the modern bus is indisputably French, I suggest using the original French word to convey the root meaning: