Actually it is technically possible: Trace would have to fail, and it only fails on Zorua/Zoroark and Arceus or another Pokemon with Trace. So because none of them can learn Skill swap (side from other Pokemon with Trace), they would have to make Trace fail then switch to a Pokemon with Skill Swap. Source: Logical deduction.
First They come out and Trace fails to copy Illusion. So Gardevoir STILL HAS TRACE. So then you switch to Spinda and have it use Skill swap. Though it would not do much good as its Trace would fail as well.