Give this a try: http://www.webmessenger.com/products/mablackberry.htm
It is a WebMessenger product called Message Alert that allows you to assign email rules like spam filters, and set rules for SMS messages and phone incoming calls. You can also have it set to vibrate and ring at the same time instead of vibrate, then ring like the default BB feature. Also, you can set the number of vibrations or rings, so I think it will work for you. You will have to set your normal profile settings to "None" though so it win't interfere with these settings. Also, you are limited to the included ring options on the program, not allowing you to use the BB ringers. That's the best option for you at the moment, I think.