Are there other 'casual outfits' available for Shepard?

If you use a save editor and change the right Boolean values to "true", you can get a total of 10 outfits.

• 22590 enables the tracksuit from the Collector's Edition

• 21752 enables four other casual outfits: injured, underwear, clothes worn during first Reaper attack on Earth, and "casual scientist outfit from ME2"

It even works on the Xbox 360 version.

No, there is no way outside of DLC/Collectors Edition or altering game files to expand the availiable 'casual' attire options.

Neither of the links below are SFW, as they are VERY causal outfits. Both require editing the coalesced.bin file to activate and are definitely not available as a normal in game feature.

FemShep

Bra and panties hack... looks like Udina's office

Nice bit of design (lace) work on the bra, too bad they didn't spend more time on (especially) her arms. A really unrealistic body type, especially for a female soldier. Conveys an eating disorder, not strength.

MaleShep

The male Shepard gets a pair of black boxers and a muscle bound physique that would make statues of Greek gods jealous. This collage shows him wandering around level 1, getting felt up by the Admiral and generally looking odd without a uniform.