Ok i was close then

- To be honest if this was me (im changing my mind slightly) id go for an email stating what you think you need to do.
Something along the lines of we agreed certain dates and you cant complete the work until you have his feedback - explain you have other projects that you want to commence and give him a deadline, say 7 or 14 days from date of email.
I would gently somehow explain what it is you expect from him and that failing to contact you within the time frame would mean that whilst you may be able to continue the work at a later date you could not commit to any set dates. Id also explain that your expecting to increase your rates in the near future and work carried out at a later date
could be subject to an increase in your fee. (if that doesn't get his attention nothing will)
If he doesnt come back to you - i really dont see what else you can do but can the project until he comes back to you & then it will be reacting i suppose to whats said - you could always post for some advice then?
I cant believe people are so blas