Though one. Maybe someone else has a way better solution, but I only know the following which has a good news part and a bad news part:
Good news to make changes easy for the future:A way is to activate CDP/LLDP on your switches if they support that so the phones auto hop to the voice vlan (whatever that might be) and get a DHCP request from the Mitel.
If your switches don't support that you could setup the DHCP server in your data vlan to include a scope and the necessary options for voice so they get an address, switch to the correct vlan, use the correct prio, tftp the software and connect to the correct call server. This way its centralized and easily changed aside from the switch config changes.
The bad news part is:Whatever you do, I think you still have to access all the phones and set the Static IP4 settings under network settings to default (0) if you plan use one of the above options of which I think the CDP/LLDP option is certainly the best way to go. But it would be the last time that you have to do it
Dutch