Setting up iPrint in an HP shop.

NONe of the hp printers they have are in the iPrint driver lists.
HP 4050, 4200

What I've been doing is setting them up as 4100 (which is in the
list), then
changing drivers from the Windows selection list.

I know there is a way to add printer drivers to the iPrint/NDPS
system, but
it looks like it only reads them from Windows-type cab files. How
would I
add ones from HP driver kits or elsewhere?