i dont know exactly for your model phone, but i know for hte phone I have there is no way to change the amount of time recording a video. I can do a max of 4 min recording. If there is no setting within your phone to extend the time, you may not be able to extend video recording.
I may be wrong, since i dont have your phone, but I am thinking you won't be able to change it.
I have the same problem with my 6600. I had one of the first phones released (with 9 sec recordings), its been stolen and the second phone I got were able to record 17 sec....untill I restored my previous phone's backup so I could have all my phone nr's again. After that it was back to 9sec.
Isn't there a version upgrade one can install? A patch in a .sis mode or something?