I have posted a similar query to the Pension advisor of our company pension i.e. Can I put my AVCs elsewhere ?
The documentation I've seen seems to say that if you have an Occupational Pension that accepts AVCs then you cannot put them in a separate PRSA.
I am looking at doing this for a different reason to you but worth looking into for youself - my company pension pays out a '33% of my salary pension' to my spouse if I should pop off at any time regardless of how much is in my fund, therefore if I AVC up to the max and create a massive fund, then die, all that AVC money is lost to the pension people. Putting the AVCs into a separate fund/PRSA would at least accrue more benefit for my potential widow.