impossible to me is:
back foot in pocket, flip it over, almost like a pressureflip, but wrap instead of letting it flip. front foot out of the way
you need that pressure to get yr board sideways so you can actually wrap.
but don't listen to me, listen to @silhouette
That's also how I first learned them (the pressure flip way, just after figuring out normal stance pressure flips) and then I gradually adjusted my foot placement over the years, now my back foot is literally flat across the whole tail and I pop completely vertically. I can still sense the tension on the toes that allows one to get a good wrap but it's more subtle and happens with the pop which I conduct with my whole foot, overall I feel like I scrape the tail a lot more than I used to which I think is an optimization of the technique for that trick, then it becomes automatic and happens in one motion (like the way Chris Athans does them) (I can't believe I almost wrote 'Chris Fissel'). I can just set up real quick, picture scraping my tail through where my front bolts are and do just that like it's a modified ollie whereas for the pressure flip style, you put pressure over the toe-side back wheel with your big toe and kind of wait for the board to react to then go for the wrap which is a bit more tedious to do and often results in the trick going sideways more.
I posted a shit ton of tips for that trick in the Tricks that piss you off/Tricks you're trying to learn right now threads, I don't expect anyone to look up my post history but they're there and probably not that far up the previous pages in the threads if someone is really looking for some.
Either way, 360 shoves and impossibles work completely differently (one is a horizontal trick under your front foot, the other one a vertical trick around your back foot) so even though some people do ugly hybrids I think the first thing would be to determine which one exactly you want to get, there is no happy medium between both in my opinion (if you're trying to do them right).
@Skatebeard for switch 360 shoves/impossibles/360 flips in general a lot of people have that problem, more often than not the fix is the same, you're probably trying to use your usual shoulder (the one you usually have at the front in normal stance and normally use for direction) to remain aligned over the board but since you're in switch stance that actually throws you off axis (as if consequently you started 'body varialing' ever so slightly to fix your stance back to regs), you probably need more focus on controlling the other one instead and also a less open upper body stance (face where you're going a tad less), and then just focus on remaining parallel throughout the whole trick.