Anyboby else know how to use apinger to monitor other IPs?
Well, you could create bogus GWs. Frankly, with the source being unavailable, the thing reporting inexplicable "packet loss" when in fact there is none etc., I would not recommend anything like this.
@OP: Get back to the APs vendor about some centralized monitoring, also, there's SNMP and whatnot, again depends on particular HW model.