I think that could work... It starts off slow, but once established, it will start growing roots like mad (if the lighting and water chemistry are correct). You will be able to tell... it will grow new stem/leaves as well as roots. When you see big time growth on the top, the bottom is probably growing too.
The thing is, as soon as you pull it out of the other tank, it will still try and float up on you for awhile. When it grows where it stays, the roots actually attach themselves to the substrate, and thats what helps anchor it.