I think you're veering way off the main highway.
And, while I hate to put you in the ditch, I'll mention one item anyway.
Dish Network made an
unstacker for their old Legacy receivers to take DishPro (bandstacked) LNBs.
But this is not a serious recommendation; more like something to contemplate.
Would it work? I'd look for any other sort of solution, first. But it might.
edit: I must've posted this in another thread (thought I'd said it here...)
See the
pictures at the bottom of this post.
They are of a MA/COM feedhorn with two LNBs.
Talk to Linuxman and see if this would be a cheaper solution.