Funkifized:

I can't see a way to enter a chord in bar in Bar -1, or Bar 0 ("Lead in") and have BIAB play it,
but you could try the Support people with the "Let's Chat" button here and see what they say.
Or perhaps a more knowledgeable Forum member will chime in.

If you have to do it "manually", you would need to enter what you needed in Notation or Piano for EACH instrument in your "Band".
Good luck!
LLOYD