Consider a possibility to provide SASL authentication for PHP ldap module, i.e. use "--with-ldap-sasl" when configure. With this option, an additional function "ldap_sasl_bind" will appear. Note, that the current ldap.so module already depends on libsasl2 (see ldd /usr/lib/php/modules/ldap.so), because ldap libraries already compiled with sasl support. It means that nothing too big will be added anyway...
This is done in Raw Hide now; thanks for the suggestion.