Don't have them, but since they just modify the existing P5 bar by extending the ends and cutting the back, here's a tip on how to save GBP299 and get the same result:
1. Go to a hardware / plumbing store or online. Buy 2x 22mm copper plumbing pipe couplers like this -
Coupler Straight 22mm X 3/4 " Copper Coupling - - Amazon.com. Will cost maybe EUR1 for both.
2. Find an old 22.2mm aerobar lying in your parts bin. Alu or carbon. Cut 2x 5-10cm sections (however long you want to extend the end of your bars).
3. Insert one end of your cut section into the coupler, and the other end of the coupler onto end the P5 aerobar. Do for both sides.
4. Check everything looks good and fits snuggly, then glue all the bits together with some super glue.
5. Wrap ends in bar tape.
Should add around 50g weight if you are fancy and use an old carbon bar for the extension.
Cut rear of P5 bar if required.
You're welcome.