DMVPN

Iv found my self a bit stuck with a dmvpn solution our current dmvpn on 2 routers not in a cluster but master and backup but also running with HSRP has reached its capacity and I need to extend it whilst keeping all the spokes connected. my initial thought was to to just change the subnet mask and update the eigrp but when i Labbed it. it dropped all the spokes because of a miss match on the subnet, so then i thought I would run 2 hubs on the same router. That caused the same issue based on using the same external ip and a different eigrp AS so now im at a loss on how to increase it. has any one done this before? be currently have 500 spokes. on our ASR 1002 and i need to atleaset double it. any advise would be gratefully received.