If it were me, I'd probably pot them all up and see which seedlings have the most compact growth with shorter internodes and then keep those and trade off or give away the rest to other crazy gardeners .
I found a photo of one in a greenhouse:
http://jardinclairobscur.blogs...
Maybe Kermit, or someone, will have some tips for pruning it so it will still bloom but not take over the entire greenhouse. I wonder if you could sort of "limb it up" so it takes up height rather than width.
