If this does go on for a considerably long time, then start bustituting the Thames Valley branches in the following order
1. Windsor
2. Greenford (its practically dead right now anyway)
3. Marlow/Bourne End
4. Henley
Use these 4 Turbos, further West to complement the services starting at Swindon.
Utilising some of the many Old Oak Common 345 sets to run fast from Paddington to Reading. Yes they're 90mph max, but besides HeX services and the current 1tph Swindon service, they can be woven into a pretty empty Main Line. Alternatively, let TfL take on the GWR semi-fast Didcot services as far as Reading and use the spare Turbos that I've mentioned above for a Didcot - Reading all stops shuttle. Deploy the 387s on more fast Paddington - Swindon services and/or wherever else they can be run.
There's not an endless supply!