It looks as though Denham - Wycombe could be the interesting part of the route. As Denham is in the London CTR perhaps a Special VFR Clearance from Heathrow westbound to Wycombe?
The Wycombe zone digs into the London TMA (2500 QNH+) to the south, but I assume Heathrow would help with that (keep an eye open for gliding activities at Wycombe).
It might be useful to use 2400 QNH as an altitude south of Wycombe - it keeps you below the London TMA @ 2500 QNH, above the White Waltham / Blackbushe and Farnborough zones (just), and below the Gatwick TMA @ 2500 QNH.
Farnborough LARS are the guys to talk to south of Wycombe and they give a great service - they might get a bit twitchy with your 2400 altitude, though.
South of Dunsfold watch out for gliding activities out of Parham.