There are IP to analog converters that can run off a SIP license. Typically these are used for Faxes but in your case would setup the analog and IP phone so that the extension ringer can be connected to the analog station.
Hopefully you have a 3300 MCD 4.0 and can utilize the personal ring groups.
Also, with a 3300 MCD 4.0 and Remote hotdesking + Personal ring group (Dynamic Extension) you could get the controller to dial a DID out and back into your system that was cannected to the ringer. Not pretty but...
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Occam's Razor - All things being equal, the simplest solution is the right one.