To my knowledge, the only variables available for the fax template are as follows:
Fax
%%CALLER_ID%% Caller number
%%STARTTIME%% date/ time of start receiving FAX
%%CALLEE_ID%% Callee number
%%STOPTIME%% date/ time of finish receiving FAX
%%FAX_ID%% FAX number
%%PAGES%% number of pages in fax...