Do yourself a favor and just snip the tips to slow them down. Wait until the newest top growth emerges like two hands praying and cut once across the base to FIM which will promote multiple tops. Let them veg for a couple more weeks and then....
Take your clones from the bottom under-growth when they get a little bigger. Clones taken from the bottom have more natural root hormone than the tips; higher chances of success. It is possible to clone short tips but unless you’ve got a bitchin aero-cloner chances of 100% roots are slim. Try to take your clones about 6” to 9” long if you can; longer is better than shorter. If you want 100% success every time get a clone king or similar unit. Last time I used it we rooted out an entire 36 site tray of clones in 5 days. No gel no powders no hormones just plain tap water. 2 drops of rapid-start will push roots faster but is optional.