You could try to put the phones behind a captive portal interface and upload your config to that, give them pass-through access for the portal since they wont be able to authenticate.
Hm... It was fun to find this reply after 4 years...
Just to understand that it will not help.
Idea to integrate TFTP server (now definitely talking about TFTP) is still actual. There is a lot of available VoIP hardware that trying to read provisioning and dial plan XML file after every restart.
One of such devices is near me right now (Cisco CP7970G IP Phone with SIP firmware installed, used with one of BYOD SIP providers).