When I bought Pegasus (P325 no 37), I was faced with same problem. 37 was built with a coach roof track and capstan set forward in the cockpit similar to your description. The original main sheet arrangement ran forward up the boom to the mast and then down and back to a clutch on the starboard side under the spray-hood. I was unhappy with this, as I was likely to be sailing with my children / non-sailors and the thought of being behind the wheel without being able to quickly release the main concerned me. After some lengthy discussions with Bill Parker the solution was to bolt a single white fiberglass pinnacle in the shape of a horn (from a Parker 21, I believe?) on the centre of the cockpit floor with a Barton stand up cam cleat and pulley on top of it. The main-sheet still uses the coach roof pulleys and coach mounted track, but now runs aft under the boom and down to the pinnacle pulley and cleat. I can now reach the main-sheet in a hurry from the wheel without delay. System works well. Further, there are other advantages to this arrangement, most notably the fact that whilst main sail control still lives in the cockpit, the mainsheet track and dangers do not and this has saved at lot of little fingers and scraped shins over the years! Further the arrangement has been very strong too and handled all weathers and I have even notice some new high performance racing yachts using the same system! Hope this helps? Will send photo if interested.
Stuart
Pegasus No 37.