I need to send out a ton of Vigor 2860's to various sites. Once they're out there, they're owned and managed by their respective site owners. I need to pre-configure each one before sending with various settings, including things like WAN settings, LAN config, Dynamic DNS, VPN users etc.

I want this configuration to survive factory reset - so that end users can reset them, and they reload with the original configuration. They probably arent technical enough to do anything other than that. The general scenario for needing to do this is when they lose internet access, and we wont have remote management access.

Is this possible?

Factory reset is exactly that - so what you're asking for is illogical. If you're buying these in bulk (as a factory batch), DrayTek can set a custom factory config as they do that for ISPs but I assume you just need a handful and there's no way to do it yourself.

The best you'll probably get is to do a copy of the configuration backup and send that with instructions on how to load it.