I don't see why they would need clearance to play in a different country anyway.
The only clearance should be at the place they are training/playing at to make sure it is free to use.
Any overseas player coming to play county cricket needs a clearance from ECB as well. You just can't walk into a set-up and ask to be played. The usual process was that the native cricket board would make a request to the relevant board to allow its player to play for a county or if a county wanted to get a certain player they would have to get something from ECB and the player has to get a NOC from his native cricket board. If this was not the case, there would have been loads more of KolPack players.
Moreover, Home Office will not issue a visa if you said you just want to come to play cricket without any sponsor or club asking you to.
I think, if I were to set-up a formal cricket coaching/performance centre in the UK (like this GCA or the MRF Pace Foundation or NCA thing in India), for it to get the necessary funding and recognition, I would have to liaise with the local county cricket set-up who will then in turn request ECB to formalize its training program. Without this why would a cricket board bother to send its players to come to my centre for training.