Would some kind of mobile walk-in physio surgery for runners be a possibility? It could cover quite a large area as it would only need to visit each population centre at most about once a fortnight -- and could be advertised through running clubs and running shops as well as through GP surgeries. It could refer people to appropriate local services where needed, but could also diagnose straightforward cases and give guidance on how to handle minor niggles to prevent more major problems.
This may be a bonkers idea (it's straight off the top of my head); but with 60% of adults overweight and >20% obese, it surely makes sense to look for innovative ways to support runners. I can't see how something along these lines could fail to be cost-negative over the longer term (just considering the direct cost to the NHS, leaving out of consideration lost economic productivity and other costs of an unhealthy population).
Running comes close to being a free form of exercise. People shouldn't be excluded from it because they can't afford private healthcare.