"My "solution" would be to fit aircon to A, C and D Stock and order extra C Stock."
You cannot be seeerious! The A stock is over forty years old. All of these classes are due for replacement (by new stock with "air-cooling") in the next five-ten years. And build some more stock to a 30+-year-old design, which couldn't be ready much before the entry inot service of the first of the new stock (2009)?
"Extra Surface/BR Lines"
"Euston DC Lines (increased frequency with short turns to replace Bakerloo intervals)" - maybe, if Silverlink has enough rolling stock and staff
"Extra stops at West Ruislip and South Ruislip on the Chiltern Line" - doable, but there is hardly a tube level of frequency on the Chiltern line.
"Liv St - Epping/Hainault/Woodford" - So you've rebuilt the connection from the GE to Leytonstone, yes, but presumably with no flying junction - interesting effects on timekeeping of the main line out of Liverpool Street. And, um, Liv St-Stratford has overhead wire AC electrification while the Central Line has LU third and fourth rail DC. Um, rolling stock for this service??
"Moorgate - Fisbury Park - High Barnet" You have put the track back between Finsbury Park and East Finchley. But again, no flyover at Finsbury Park, with baleful effects on everything out of Kings Cross.
Again, what sort of electrification? What rolling stock?
"Moorgate - Kentish Town - Barking (DMU alternative to Victoria Line)" - Um, Murphy's builder's yard goes over where the south-to-east curve north of Kentish Town used to be. Murphy's just might object to the track going back in.....
"Liv St - Chingford increased service" - doable, provided that the rolling stock and staff are available.
And all of this just for two months a year until a solution to a/c on the deep tubes is found. But then, you were only joking, James, weren't you?