I'm embarrassed to be the only one not to solve this so far...
It's the dang ending that's driving me crazy. If there were a blue sphere in the barrel, then I'd have a perfect solution, but it seems there's a green or yellow one in there, and I'm stumped. Also have no idea what I'd do with the barrel even if I COULD move it.
EDIT: Just had a new brain spasm and thought of a possible solution. I'll report on my progress in 5 minutes!
EDIT2:
I made it! 
That was one complicated level. But I feel like I know it like the back of my hand by now. Time to call it a night.
Thanks for the level Mark; it was exceptionally well-crafted!