Caller ID Issue

Some clients are sending callier ID as alphabets but our provider doesn’t support callier ID as alphabits. we can only send numerics. i want if client is sending alphabats asterisk should set privacy:user
exten => _X.,1,SIPAddHeader(Privacy: user)
and if caller id sent by client is numeric then it should be forwaded to our service provider. to forwardard caller id from client we are using
exten => _X.,2,SIPAddHeader(P-Asserted-Identity: tel:${CALLERID(num)})

Please help me out how to write the rule in

Take a look here