Make a hole on the side of your TomTom. Find the place where you can lead the cable out without damaging other electrical elements and without making the connection fragile.

This is the way it looks at the moment. It works. Insert another USB extension cable and you can put the GPS element wherever the reception is best.

Of course a little box to put the GPS antenna in makes it all the more aesthetic and robust. I simply glued the cable to the metal of the GPS element and will probably stick it to the window with a two sided tape.

I guess the antenna works best with the purple element directed to the sky.