Different clones different stages?

I have several clones I have taken into veg 15 days ago. I have just been given 3 new strains that have just rooted. I would like to veg and flower them together. Is there a way to hold off growth on the previous clones until the others catch up.? I assume I could take them out from under the halogen lamps and put them back under flourescents. Any suggestions? (part of the problem is I have a height constraint and am afraid the initial strains will grow to big)

Hmm I'm not sure about your halogen lamp, maybe your talking about hps? In any case you can always do some trimming, topping, or lst to keep them short for the extended vegging girls. Also you may consider running them staggered so that you don't have to harvest them all at once. For me it makes it easier this way and I find I have bud for longer since I have different stuff at different stages.
KnB