You can always make a PNG frame in Photoshop. I assume a frame made in Titler is not what you want.
As Cvid suggests, I create my "frames" in Photoshop. Not sure about all versions, but my PS has several Actions, just for frames, and I have made a few more, with a different "look."
I Save_As PSD, and just Import those as Footage (I do not need the capability to work with the individual Layers).
If you want your pips to be sqaure you will have to crop the clips first.
Then go into the Title and make the frame as pointed out by Peter, very easy and very quick.
For more then 1 frame, Alt drag the frame and just change the color.