I think a lot of it is just practice. I've been practicing, and I'm getting rather good at it. I can tuck pretty quickly just standing in front of the mirror. I like holding the penis in place from the back and looking at myself - lets me imagine what things might be like post-op.
Anyway, a friend has told me that control panties are the way to go for holding things in place. Of course that won't work with a bikini, and I have to say, I applaud your courage trying THAT. But I assume you're a lot younger than I am, and better looking, lol. Not sure I'd try tape, but Yubel has given you good advice as well. Good luck!