I went with my own idea and decided to upload it. It ended up being a complete rewrite of Blizzard's StackSplitFrame. I was able to allow keybinds to run by switching
frame:SetPropagateKeyboardInput() and I added a couple more control methods as well. It loops the callback to allow processing as many stacks as necessary, though there may be an undocumented limit to how many stacks can be purchased at once.
StackSplitPlus