Ok, I found it, you can do it like this:
new InlineMethodProcessor(project, psiMethod1, null, editor, false).run();
new InlineMethodProcessor(project, psiMethod2, null, editor, false).run();
Incidentally, now that I've done 2 refactorings, they result in 2 undo actions.
Is there a way to "wrap" them (and other things) into one undo action, I wonder?