The correct answer is channel. (One third party support company named itself for this, the covalent bonds in chemistry.)
Actually, Dave, it's creating a channel.
It's customers who are reluctant to support third party open source support. I was shocked several months ago when SpringSource bought Covalent, a third party support outfit. Shocked that SpringSource was so much bigger.
Where would Microsoft be without third party support, those ISPs and VARs who extend its reach into places it can't afford to go?
Channels like third party support companies need to be nourished, not feared. Offer their people special classes. Give them special badges at your own support events. Throw them a party, buy them a beer.
It's true that, at first blush, you seem to be competing with third party support companies. You see a dollar going into someone else's pocket and you're not even getting a taste.
But those companies are dependent upon you, for most of the improvements they're selling. Their existance is a vote of confidence in your software. They want to give you a taste of that dollar in their pocket.
Capitalize on it.