What version of 2.2 are you FRG01b, FRG22 or FRG22D? or a custom ROM?
If you are a custom ROM then go to the site that is home to this ROM and see if there are instructions on keeping away OTA notices.
Otherwise read on.
I am currently sitting at FRG22D Rooted Stock Odexed. Mine is the Stock ROM available from metiCkOne.
IMO if you are running a stock rooted Froyo either FRG01B or FRG22 then there is no reason you shouldn't update to FRG22D as there are Rooted options available both Odexed and Deodexed.
The three I know of are metiCkOne, Pete Alfonso(Bugless Beast Fame) and P3.
P3's ROM was a very early ROOT and was rooted differently than the other 2 and people have talked about issues with it.
I had used Pete's FRG01B and was very happy with it. I went to metiCkOne's FRG22D because his was out at the time and was reported to be pretty stable. Pete's FRG22D was a little latter in arriving.
I will tell you that I did not Wipe Data before I updated from FRG01B to FRG22D and had no problems. I will not get into this area of wiping data as everyone has an opinion on it. But going from same Version to Same Version as in FRG01B to FRG22D the consensus is that there is no consensus. Wiping is best best practice but up to the user as to what they feel safest with.(in going from a stock root to a stock Root, I think that is safe not to wipe as neither ROM has been extensively modified, It is the customs that have had extensive Ground up Mods or been rebuilt from the ground up that could give you the most trouble if you don't wipe.)
There is not much to FRG22D and it is really not that much of an upgrade at all and most people say why bother.
My thought is why not. Also I have 2 compelling reasons to upgrade.
1. It gets rid of the nagging requests to update OTA which you are complaining about. By the time your done fooling your current build into stopping OTA's you could have just updated with less fooling with the software.
2. Even though you can directly download and install Flash and bypass market and not need FRG22D, you loose out on update notifications (or if you want Automatic Updates) that you would receive if you had downloaded it from market and had the update push for Fash that comes with programs that have been downloaded VIA Market. (There has already been 2 updates for flash) After installing FRG22D and already having Flash I still went to Market and redownloaded and installed it and checked the box for Autoupdate now one less thing to keep on top of.
So given the rather Banality of updating to FRG22D and the advantages why just update and leave behind any OTA notifications to do so?
For me it was a no wipe 10 minute process through ROM manager. (I did do a ROM Backup.)
Here is a thread I started on Rooted Stock ROMS for FRG22D and the info gleened from it.
http://androidforums.com/droid-all-things-root/166584-frg22d-odexed-deodexed-available-pete-alfonsos-page-any-info-them.html