Well, I think I found the answer:
-f FEE_PERCENTAGE, --fee FEE_PERCENTAGE
charge workers mining to their own bitcoin address (by
setting their miner's username to a bitcoin address)
this percentage fee to mine on your p2pool instance.
Amount displayed at
http://127.0.0.1:WORKER_PORT/fee
(default: 0)
I'll try some experiments...
Anyway, if you could recommend some other open source pool to run would be nice.
Regards.