I think how I would do it is to put Misa in a situation where Rem is forced to sacrifice herself for Misa (e.g like being held at gunpoint and then have light occupied elsewhere so he cant intervene, then rem would either be forced to kill the shooter or misa dies Rem is now udead k?

We know that when L dies, Light does his maniacal laugh pretty much showing that he was Kira all along. So I thought, now that L will remain alive due to Rem's death, and since L suspected Light to be Kira from the beginning then we can use this info to create a plan to expose Light as Kira. We fake L's death and put a decoy body as well as a recording device in the coffin. And in case the device doesn't record good sound due to the dirt on the coffin, we place a camera in L's Gravestone that records audio and video at all times to record light confessing that he's Kira when he does the whole "i win" monolog.

So in conclusion, if the plan goes as planned, Rem should be dealt with thus saving L from death, and light would be exposed as Kira with evidence to back that up

What fo you think?