Cessnaboy
Dont know if this helps but if you are already a CAA AFI you can upgrade to JAR FI (sort of equivalent to QFI but without the ability to teach IMC)with 100hours instructional (excluding trials) plus 25 solo flights briefed and a fee of £55. Cant help with details on converting a foriegn instructor qualification but a JAR FI course will cost about £4K.
100 hours a month during the summer is perfectly possible due to more daylight, I did 90 last month but that compares with just 35-40 during Dec,Jan and Feb. This however is at a controlled field with rationed slot times even for GA traffic, a club strip would afford even more work.