The best way is to use a Tx with more than 6 channels and aditional proportional levers like the 9 channel JR system wchich has two aditional proportional levers or sliders and can be used for this particular purpose.
Other way is to use the throtle and one aditional channel to mix with, definitivly you need a computer radio.
I have seen the new advertised Hitec 9 channel radio on some magazines, I bet that it could be capable of doing so at a fraction of the price in comparison with the two leader brands.

Good luck.