slightly easier than what you suggest:

Logjam > Preferences > allow multiple instances of logjam & automatically save drafts

Then compose entry, and open a second instance, you will be asked if you want to load saved draft, say yes. Change user to whichever one you haven't got chosen, then post and close both instances.

...looking at it like that, I'm not convinced it is actually *easier*, but it seemed easier to me.