How can I manage a tall lanky sativa indoors?

Firstly you do need enough height. If you have that they will need supporting and the best way is with a devise we call a yo-yo. This is a sprung loaded reel with about 2 meters of line in it. It has a plastic hook on the end.

The Yo Yos one for each tall type plant are hung at the top of the grow room and the hook on the line is pulled down and hooked round the the plant stem as soon as it starts getting tall enough to be floppy. As the plant grows it is wound round the line and the spring tension keeps the plant growing upright and straight.