The power converter used in the DSC and the first public revision of the analog breakout module meets the requirements for this task. An ugly but effective hack would be to power one of these with the dedicated (boosted) 12V supply from the PD, and use that to power the radio.
However, there are some drawbacks:
- This suggestion is not legal by current rules.
- The circuit couldn't/shouldn't be used for anything else.
- It is super ugly.