I can actually imagine it might even be easier to use a pack & pee pre-T. So before downstairs growth. Since you're not peeing from your clit, I imagine it could only be in the way. Compared to pre-T anyway.
Anyway, you can just sit down in the stalls, that's no problem. A lot of guys actually not only use stalls to pee but also sit and pee. And if someone would find it strange, you should just look at them as though they are very creepy themselves. Because why would he pay attention to your visit to the toilet!
That said, I'd stay away from the Mango products, because you can make those yourself and it will be a lot cheaper. You'd need a Mr. Limpy softpacker, tubing and the recepticle of your choice (medicine spoon, baby bottle nipple or something)
Edit:
Oh btw, to 'prove' it's possible to use a pack 'n pee pre-T. I'm pre-T (and a long way from it) and I can use multiple STP devices.
