I've done some work on this in Dolphin just now. The "magic frame", at least before the text, is this:

(I've tested it on both the PAL (25fps) and Japanese (30fps) versions, and the frame is identical in both, with no reason to assume NTSC-U would be any different.)

Because this frame is while Mario is still in the air, the only things that can be done as far as I know are pausing, switching the nozzle, and opening the map.

Has anyone managed to get an input in on the frame after the text?