I haven't been presented with this predicament... yet...

A few years back I got my Comm. AMES in a Widgeon, it's got a tailwheel. I'm interested in getting my ATP add-on (if I can get some spare change!) I don't have my tailwheel endorsement, so the way I look at it, I could spend 20 hours (exaggerated) on the lake with the instructor doing splash-and-gos and not be able to log any PIC... Since the Widgeon is a tailwheel and I haven't got that endorsement.

Am I right?

Obviously the easiest answer would be to get my tailwheel before I go down there. I can't get it in the Widgeon... The owner won't do it bc he doesn't have right-side brakes.