I haven't seen either. I mostly just stick to writing code for customizing surveys - I can't comment on what ends up out there or what best practices others are doing. Someone else on this forum might be able to offer more insight there, but my guess would be that it wouldn't be a big deal as these are just practice questions rather than your actual MaxDiff.
That said, to implement the two-exercise option, you just need to include this in your second exercise:
SSI_SetSelect('[% QuestionName() %]_b_[% mxd1_1_b %]', true);
"mxd1" should be replaced with the name of the first MaxDiff exercise.