I was going to recommend the same... The phone should use the mic on headset for any recording function when plugged in... Maybe a higher quality mic would be an easy workaround until a possible software fix is available.
This now makes me wonder if a BT headset would work. It would be pretty cool to be able to have a remote mic in some situations...
on another note, it would be cool if there was an app created to use you BT Headset for recording and also be able to listen from the phone as if you were on a call... Once you initiate the app it could give you a minute or so and then fake a call to you. You take the call and mistakenly leave your BT headset on the table. You excuse your self from the table and walk a reasonable distance away (within BT range) and listen in to see what people have to say. I would buy it!!!
Sorry for the off topic rant... Kind of related with the BT mic recording but not really...
Now, something else just poped into my head here... I did a google search on 3.5MM Mic and BAM!
Not sure how good it is or how well it will work, if at all, but the design that allows you to point the mic in the direction of the source has got to be better than the onboard mic that is located at the base of the phone which we most like have covered with our hand when recording.
I'm sure there are better out there as this was the first one I came across but here is the link:
http://www.davismicro.com/products/product_6966.htm