That would be fine.
Infact. That is the best way to flower sativa's.
From Clone.
Otherwise your lant would touch the cieling.
The only reason he said to grow it outside.
Is the hieght and long flowering time.
But your plan will work.
Thats what I do with big sativa's.

Keeping it under the floro's is a good idea.
Just let them root real good.
Thats the key.
And raise the light about 12 inches for the first couple days.