In terms of a transfer, assuming the analog modem is going to actually work (a significant assumption although I haven't tried it on any of the more recent firmwares) you would have to connect an analog station port to analog trunk 1, and live with only 3 analog PSTN's. If that is OK, then just transfer a call to the analog extension which is looped to trunk 1 which is configured to answer with the modem.
Peter