What I would do is take what you have, cut 1/16th of an inch off he cut part, dip the cut in rooting hormone and try rooting it before you put it in the tank. Put it in a well drained peat based medium and it should root within a few weeks. If you can put it in a 1.5-2" plastic pot you could simply leave it in the pot a while, then pop it out of the pot and plant the plug in the ground of your Vivarium. Just make sure the plant dosen't stay to wet or in direct spray of mister nozzles, they may get leaf rot if they stay wet too long. Good luck.