I think there are a few options that would work for you. Do you currently have a quick release system for your tripod? If so, you may be able to find something that will use your current quick release plates. I have a Manfrotto 234RC Swivel/Tilt head on my monopod. I will tilt forward and backwards but it doesn't give you the full movement like a ball head would and if you don't want it to move at all, just tighten it down and leave it. For less than $40 it's a pretty good piece of equipment that should fit your needs.

If that's too much, you could simply by the clamp with the plate like this.

http://www.amazon.com/Manfrotto-323-...3714855&sr=1-6