How to assign two extensions to the same obi302 device in Ring Central

I am migrating from AT&T Collaborate to Office@Hand. I have an analog conference phone and a fax line going to my Kyocera MFD. Both were tied to a single obi302, one on each analog port. How can I recreate the same situation under RingCentral. It is only allowing me to assign the single device to one number at a time. I don't want to have to spend $$$ for another conference phone.