There are basically 2 ways:

1) hack your front end. EricMPro on here has done this to at least one or two P5s and some other bikes. I don't know the details, but involves doing something like what you've already done, just more of it. Personally, I don't like that for a long term solution as I question it's strength with how much force is imparted on that area.

2) buy a new aerobar system. No aerobar system will integrate perfectly into the front end of a P5-6 except 3T's Aduro (your stock setup). People have come up with clever ways to keep the beard and attach it to their new aerobar of choice, thus creating what appears to be a 'stock' P5 nose. But in reality, you are not losing much aero NOT having the beard/full integration (probably). You make up for anything lost there with potentially a better position. The P5-6 can be very reach limiting, and it's hard to pick the perfect size until you have a lot of experience with the bike. I rode a 54, but felt reach limited after a year or so. But of course, not an easy thing to replace.