Yeah, I've done it a couple times with coke. Put 100-200mg in a gelcap and shove it in. It worked quite well for me both times and I would definitely do it again in the future. The onset is slower (~20m) and the high is not the rush you get from takin' a big ol' line. However, it lasts a lot longer -- maybe 2 hours at the most, and the comedown is very soft compared to any other route.
My recommendation is to use this method to keep you above baseline for the duration of your coke-session, especially if you are going out in public and can't lay out lines on the bar or something. Since bullets never seem to give me enough of what I'm looking for, so this helps to keep me "up there" longer.
The last time I did it, however, I put too much in the gelcap and ended up getting a shakey stomach from too much coke. Start on a small dose and get used to using a small dose before you climb the ladder.
But if you're just sitting at home (or someone else's house) and blowing with friends, lines are the way to go!