On the config page there is a section that states there are variables like [ClientName] and [ClientEmail] that can be passed to URL fields. It doesn't seem to work for the Custom App Download URL fields. I use Simple Help remote desktop software, which generates an EXE on demand. So I can pass the download URL some variables like name and email and have the client auto connect, rather than prompt the user to enter these fields.
I don't know if this is a bug, or a feature request. I know not many users will need this ability in the Custom App Download URL fields.