seatpost slipping: suggestions?

[Climb01742]

so here's my situation: aluminum post in a steel frame. and it's slipping.

originally it was just post in frame. after having it slip considerably, i applied grease inside the top of the seat tube. this mitigated the slippage but it still loses a few mm's each ride.

any suggestions for further fixes to keep the alu post from slipping?

one option, adam hansen uses a second seat collar. thoughts?

http://www.cyclingnews.com/features/...lium-sl/297688

another option is to try another post. but it's a 31.6 post and only other one i have is carbon. if i try the carbon, i assume i should clean out the grease from the seat tube and apply carbon paste? any downside to residual grease mixing with carbon paste?

to sum up my situation in a word: help!

thanks!