Maybe it's time to delve into flight modes. If you enable flight modes, you could activate all 5 of them giving you 3 normal flying modes plus 2 extra switch positions on a 3-position Flight Mode switch to control 2 more mixers that, when used in conjunction with the Channel Xpander, might just accomplish what you want.

Just as an example which may, or may not, apply to your set up, you could have one Flight Mode (FM) setup for Takeoff, one for "Flying" and one for landing. Then the other 2 FMs could be set up the same as the "Flying" FM with the addition of activating a Pmix/Xpander to drop the bombs.

Len