You'd be wrong, though. He considers it a legitimate alternative to "not releasing source at all":
> I consider selling exceptions an acceptable thing for a company to do, and I will suggest it where appropriate as a way to get programs freed.
And in fact, it could be argued that it's better (for rms' goals) than MIT/BSD/etc, since the proprietary license will impose some restrictions on its usage by other proprietary vendors.
Remember also, Stallman and co. did come up with the LGPL, which itself is a pragmatic compromise to allow GPLed libraries that can be used in non-GPL applications: under LGPL, you have to share any changes you make to the library itself, but the rest of your application can use a different and/or proprietary license.
It's better to have some GPL rather than no GPL.
Nothing about the GPL stats that you can't _charge_ for your software, in fact RMS explicitly encourages people to make money from free software. You just can't restrict the buyer from redistributing it once you sell it to them.
As to your question, you've already agreed not to charge for your patch by the fact that you've utilized the GPL to access the code in the first place. That's one of the points of the GPL after all.