Just to be clear...
You most likely can't run the RUU for the Sprint Hero from the computer and have it apply that ROM to the phone with a goldcard. The problem is that the software on the computer is going to check to make sure that the device is a Hero200 before it even starts.
However, you may be able to run the RUU for the Sprint Hero, find the temp files... locate the rom.zip. Copy it out... put it on the sdcard with the goldcard, as the device specific filename PBsomething.ZIP, and it MAY load it that way. Depends on if it checks the file within the zip that says "this is for a Hero200". You will not be able to modify anything in the rom.zip file though to make it for a different device.
When you boot into your "goldcard mode" (for lack of a better term in my brain), are you able to adb into the device? If so, are you root? If so... you can just apply a recovery.img from there.