If you can front boardslide you should be able to back lip, it's a really similar and actually I learned back lip first and that helped me with front boards.
As for ollieing on to FB that's one of those things I think you just have to commit to, so if you can get those back lips first, on boxes, I think that will help you. I never did the "shifty" technique and I don't like doing FBs on "ride-on" features because that makes it easy to pussy out at the last instant and avoid that commitment, so my advice would be to A) get that back lip down on boxes then possibly rails if you want, and then B) start working on front boards on ollie-on features.
You'll probably find 270 on will be easier to do than 270 off (I can't get that 27 off yet). You could start with a 180 on and kinda shifty/pivot your way in to the 270 position. I think that working on flatland tricks like butters (e.g., can you do a nose slide on the ground and pop 270 out? If so, 270 off rail feature should come fairly easily. My approach is to work on the buttering first and then step it up to boxes then rails this year.) Obviously you should be comfortable spinning 360. For me, frontside spins on to the features have been pretty natural, I should start working on bs spins, too.
You'll find the 270 on will also compliment the other skills you're working on (I did my first back lip, front board, and 270 on all on the same day), because the 270 on will put you in a very similar position as front board or back lip.
Last edited by david_z; 12-24-2012 at 08:08 PM.