It is certainly possible to have the Beo4 in permanent link mode provided your Beo5 provided your Beo4 software is at least at version 5.0 or later.
When it is this mode it will send the "Link" command in front of every command with teh exception of pressing the "TEXT" button.
To put the Beo4 in Link mode follow these steps:-
Press STANDBY and LIST button at the same time
Press up/down until the display shows "CONFIG"
Press 2, 0, 0, 2 and then the display will show "LINK ON"
Then press EXIT
Use the same sequence to make the Beo4 show "LINK OFF" in the display
NOTE: When the Beo4 is put into link-mode it will only be able to control TV's which are set to Option 4