There are, I believe, 2 options:
1) They sign with you, but must sit out a year. They retain 4 years of eligibility, so it is almost like a RS.
2) They go JUCO. Basically, you pour effort into them, but they may opt for JUCO. Next recruiting period, they are eligible to be recruited once more. Unfortunately, you only get a small advantage on them, and others are free to recruit them, so you battle twice.
Obviously, it is very risk/reward. If you can land one, it is great. You can get a stud, usually on the cheap, and get a free RS on him. Or, you blow a third of your budget on him, and he goes JUCO. Then you open yourself up to losing him again, this time to a rival.