A good clean with the wheels off is your best option i think.
Take the wheels off the car and clean them one by one if you can. Use AG clean wheels or Bilberry to get the dirt off. Once done you can seal them with something like AG SRP followed by AG EGP and maybe then a wax. This way they should be easier to clean each time.
Theres special wheel sealents online that can be brought, But i wouldnt want to spend an extra tenner if i could help it, So just use Auto glyms stuff if you already have it.