Here's some feedback from URC tech support:

"You would have to get the Hex Pronto raw data from the manufacturer and then copy and paste the data in Universal Browser for the command then drag it to the hard button on the remote. This would have to be done for each command you wish to add. The Hex Pronto format is usually something along the lines of the following:

example:... " (similar to above, starts with "0000....ends with....06d9" was a png picture)