This is gonna be weird, but in my personal experience, I tend to just dilate while sleeping.
I just take panties and put a panty-liner on it so that any excess lubricant doesn't get all over the place.
Then once inserted, I'll lie on my side and bend my knees. It's my favorite sleeping position, plus it helps keep things in place.
Oddly enough I'm now starting to dilate again and it's painful again because I haven't done it in over a year. Basically I stopped dilating after being a year and a half post-op because I was with someone for almost a year and we were very sexually active, so I didn't need it; but we broke up a year ago and I was already in the mindset not to dilate until I started feeling tightness a few weeks ago, so I'm starting to dilate again until I can stop dating guys too shy to make a move. >_<
So I'm dilating again, but I usually take a sleeping pill before inserting to knock me out quickly so I don't have to deal with the pain. :-p