Need help in creating a duplet

This is a tricky one! The only way I now to select a duration that cannot be represented as a single note is to first change the duration of the measure to be 9 beats long, make sure it is empty so a full measure rest appears, then select *that*. So, for instance, assuming your score is actually in 12/8 time:

1) select the measure you want to contain the tuplet
2) hit Delete to clear it
3) right click, Measure Properties
4) set actual duration to 9/8
5) press Ctrl+Shift+Delete to replace the normal duration rests with a full measure rest
6) Ctrl+8
7) change actual duration back to 12/8

There might be an easier way, but this way at least works. I can't claim credit for it; I remember lasconic (I think) suggesting something similar a while back.