"Up" and "Up (held)", for example, are not two different buttons. They're two different states of the same, one "Up" button: the "Up" button, shortly pressed - and the "Up" button, remaining pressed for some time before its released again by the user.

To create an "Up" button event (which is referred to as "plus" for historic reasons) , you could f.ex. use

tell application "Remote Buddy" 
scriptremote button "plus" event "press" 
scriptremote button "plus" event "release" 
end tell

And, to simulate a long press and create an "Up (held)" button event, you'd use

tell application "Remote Buddy" 
scriptremote button "plus" event "press" 
delay 1 
scriptremote button "plus" event "release" 
end tell

Best regards, 
Felix Schwarz