Well thats one way, but bigger chargers can also discharge too.
If you are going to be sticking with NiMH for a while (rather than upgrade to Lipo) then I would advise getting a decent charger. Makes a huge difference to your batts and performance (well, it did for me anyways!)
Before I got my discharger, i used to run my car till it stopped from flat battery, then pick it up and it will run with the wheels off the ground - keep it spinning until it stops again, and thats the battery starting to get flat. Its the best you can discharge without a proper discharger I think.
If you want a good NiMH charger, I have my old one if its any use to you.
Thing is, Annsmann make a great charger which does both NiMH and Lipo so you might as well get it - it means you dont have to change charger when you upgrade to Lipo.