You can do this currently with an "Info Box"...having it show only One Pane's indicator values...and pointing it to the pane number that contains the WPR indicator. However, you can't currently hide the line that shows the date/time. This might be an option we could add to Info Box for the next release, giving you the ability to easily show only one indicators values as large as you want in a one line text box.
Another method that you could use....is to setup a Custom Column that shows the WPR. In the "Calculations" tab of the custom column, set it up to "Place Calculated Result in Variable: V#1 (or whatever V# you have available)". Then, in the Annotation indicator, use the syntax WPR: %V#1 for the text and then in the chart, you'll see something like this WPR: 45.2