I think that "No" in the last post could read "Maybe".
Somewhere in his current backlog Paul is working on an SR3-15 for me to do exactly that!
However, it depends very much what sort of load you put on to the Mini. Mine is minimal- I use it only as an audio device, and a) it has an SSD in place of the HDD, b) the Wi-Fi/bluetooth gear has been removed. (If you want to know why, see Item Audio's site).
I have made a string of measurements, and for anything I want it runs well below 2A at 15v. The measurements are hard/impossible to do with the standard Mac white brick supply unless you break into the cable, but if you use a different supply you can get a useable cable with the Mini plug from Carnetix- it does not have a shield connection, but that is not essential.
Item Audio do a very cheap 4A linear supply to go with their modified Mini. It's made by Rapid Electronics, and you can get it even cheaper elsewhere- I have found it ideal for playing around to check out what I needed, and yes, the audio is better than with the white brick- that's what encouraged me to go for an SR3.