Programming a Softkey for Conference Line + Bridge Number on Yealink T27G Phone

Our office uses Yealink T27G phones. I want to program a softkey for our conference line that will also automatically dial the bridge number after a short pause. I found what I thought would be a solution below:

-      Log in to your telephone directly by directing your browser to its IP address (do not use the provisional landing page).
-      Go to DSS keys.
-      Create a new SpeedDial entry.
-      Everything that is not the primary phone number needs to be put in the Extension field (not in the Value field).
-      Use <#> as the pause sign, where # needs to be replaced by the number of seconds you would like to wait. For example, you would use "<4>" for 4 seconds, etc.

So, if you wanted to dial your conference line at 1231231234 and then wait for 1 second, then dial bridge number 567567#, you would put 1231231234 in the Value field and <1>567567# in the Extension field.

However, when I go to program the DSS key, the Extension field is grayed out and will not let me input the pause and bridge number. Is there a way to activate the Extension field so that it is not grayed out? Or is there a better solution to programming my softkey?