There is a third party app called CyanDelta and it gives us custom ROM end users an OTA-like experience. Sad thing is, this will only work on official ROMs from CyanogenMod.
OmniROM is using the Delta method as well to update their users, it's built into their ROM.
I'm not sure how difficult it would be to enable your ROM to be compatible with CyanDelta, but the developer states to contact him if you're interested.
This method saves time and bandwidth, especially for people using their limited data connection.