Colts are pretty easy to frag. When I had one, I cut down, in most cases, just to make bigger frags, but you can cut across at the base as well.
Make sure to take it out of your tank before you cut it. Colts are really slimey, and when cut will send a lot of slime out.
IME, the bigger the frag, the better, and more likely the procedure will be a success. After the frag is cut, you can attach it to some rock using a plastic toothpick and two rubberbands. I have attached an illustration to show what I am talking about. Basically, poke the toothpick through the base of the frag, and secure each end with the rubberbands. The frag will usually attach itself to the rock in a week or two.
Good Luck!