I was, mainly since I've faced pretty much the same issue when filling bottles from keg, when using long necks.
If you're just looking to use the keg instead of a bottling bucket, I don't think you'll need even 4psi to do the job. I typically do transfers with 2-3psi (tops) be that from fermenter to serving keg, or other vessel.
I've used the Bowie Bottler as well as the Blichmann Beer Gun to fill from tap/keg. I like the Beer Gun better. If your DIY is closer to that, then I don't see where you'll have an issue. Just be sure to get the priming solution mixed well. You could pour it into the keg, then rack right onto it (I'd use the liquid post of the keg for that to prevent oxidization and seriously reduce contamination/infection risks/chances). With the keg being stainless, you have even less to worry (for high temperature solutions going into it).
Once you're done, and they've had enough time to carbonate, post up.
BTW, I'm planning to force carbonate my BIG brews from last year and early this year (a 12% wee heavy and 9% old ale). I'll be setting them into the basement, where it's cooler and just leave them on gas until I'm ready to bottle (2-4 weeks from now). Of course, I'll have to pull a sample first.
I'm also only looking to bottle a small part of those brews. Since I have some small (2.5 and 1 gallon) corny kegs, I can simply take a small amount with me where I want to bring it. With the lower temperatures in the basement, I can even serve it right from there.