The simplest way to accommodate a pilot emergency parachute is to delete the seat back. Install the seat bottom as per the plans, but extend it all the way back to the cockpit's rear bulkhead. This will leave a large, wedge-shaped space to install a PEP. A side benefit is increased leg room. All the major manufacturers (Butler, Para-Phernalia, Strong, etc.) make wedge versions of their PEPs. When not wearing your PEP, just Velcro in a wedge-shaped cushion.We are thinking of adding a ballistic recovery for that reason. Also, a redesign could incorporate a seat that accommodates a softie parachute and is slightly adjustable.