I got the lufthansa M&M card recently and will soon have 55k miles in my account.
I've been thinking about how to maximize the stopovers on from the lufthansa program. Since they are only allowed on two zone awards and can't be used in the zone you start, I'm assuming this will work
buy SFO-HNL using BA avios or other program.
with M&M, Book
HNL-SFO on United
stopover at SFO
RT SFO - domestic destination
2nd stopover at SFO
SFO-HNL on UA again
So this way you can have two round trip flights with one award.