Really, the best and cheapest, thing you can do is modify the servos just as admin's servo tutorial explains. It's really not hard to do, and you will spend more time and money trying to figure out away around it.
There are even tutorials out there on how to save the Pot from your altered servos by switching it out with resistors. Don't bother with any of that, as it's just not worth the time or headache, and you'll get more out of spending that time programming, adding different components, and coming up with your own designs.
I am all about saving a few dollars, so let me know if you want a few tips in that arena (My $50 robot actually contains less than $10 hardware), but take my advice and just modify the servos.