Built the Tubescreamer using the vero layout by Trochy. Checking against the Screamer+ schematic from John Greene you can add a Boost pot & footswitch like this. The two wires to the boost board from the main TS board are the ones labelled Drive-2 and Drive-1 on the bottom left of Torchy's layout
Apologies if this has been shown before ...
(http://www.indyguitarist.com/torchy/Distortion_Overdrive/Tubescreamer/screamer.GIF)
(http://i30.photobucket.com/albums/c345/stompbox_layouts/TSBoost.gif)
To make this a complete Screamer+,
1. Pin 2 of the chip goes to a 47nF cap. Change it to 100nF.
2. The 4k7 resistor connected to the cap is changed to a 3k3, and the top leg moved one strip down to ground (from Vb).
3. Change the input cap from 22nF to 100nF.