Granting/denying access according auth-method

Dear list, I'm using freeradius 3 almost in standard config with mysql as storing facility. I have PEAP an EAP active. Usually EAP via TLS or TTLS/PAP is used, because the passphrases could be stored in SHA-1 encryption. PEAP is sometimes necessary for me too but it uses MS-CHAPv2 which needs cleartext-PW. Due to this I would like to restrict authentication vis MS-CHAPv2 and reactivate it when needed. I would prefer to do it via the radcheck-table for quickly activating and deactivate is easily. I read that it's possible via users-file, but I can't find any useful information/manual to me what to fill into the radcheck tables. May somebody have the idea or manual I need to follow/read? Many thanks in advance and best regards Jens