Not really, just need to specify the address of the Telstar stream:
mame dragon32 -cart prestel -bitb socket.glasstty.com:6502
The current Prestel (serial device) cartridge just needed a tweak to set the Rx/Tx clocks, they're hardwired using a ripple counter to 1200/75 baud.
(Also have Telstar accessible from other computers BBC, Electron, CPC464, Spectrum)