What can be used as formal euphemism of "hack"?

I would go so far as to say that unless you are very sure of your audience, you should not use "escamotage" at all, as it is not in broad circulation (0 hits at the Corpus of Contemporary American English(COCA)) .

If you don't want to label it a hack, a short descriptive phrase such as "short-term patch" or "temporary workaround" that emphasize that it is not a viable long-term arrangement should be suitable.

I' have seen the term quick fix (119 million google hits) used in similar circumstances. It has all the connotation of "not optimal" since that would require time for properly engineering a better solution.

Expedient:

(noun) Something contrived or used to meet an urgent need; a means devised or employed in an exigency: Use any expedients you think necessary to get over the obstacles in your way.
(adj) tending to promote some proposed or desired object; fit or suitable for the purpose; proper under the circumstances;

(sources: The Free Dictionary, Dictionary.com)

The etymology of expedient, from the Online Etymology Dictionary is from expedite:

expedite (v.) Look up expedite at Dictionary.com c.1500 (implied in past participle expedit "accomplished"), from Latin expeditus, past participle of expedire "extricate, disengage, liberate; procure, make ready, put in order, make fit, prepare; explain, make clear," literally "free the feet from fetters," hence to liberate from difficulties, from ex- "out" (see ex-) + *pedis "fetter, chain for the feet," related to pes (genitive pedis) "foot" (see foot (n.)). Compare Greek pede "fetter." Related: Expedited; expediting.

Some definitions indicate that an expedient conveys a sense of reduced moral interest, particularly a sense of being used in one's self interest, but the etymology doesn't show this. At the same time, other definitions (some given above) suggest that an expedient is less about perfection and more about making progress. Thus it may be a stopgap, a makeshift approach, a hack.

I use expedient in technical reports in the same or similar way to your need. Here is an example:

As an expedient, noise was pre-whitened and orthogonalized in non-real-time software. This was done to avoid the cost and time it would take to implement a hardware solution with the limited resources that were available. This can be shown to have been done without introducing any bias in the final results.