I discovered sooperlooper a few days ago and I use it with a self-made usb footswitch done by breaking an usb keyboard and soldering a 1/4" to two lines. Because I was a little bit unlucky I ended up soldering the numlock key lines so when I press the pedal I end up with a numlock key press.
I tried to bind it to the sooperlooper "record-or-overdub" function without any success, so I digged into the sources that by the way are very well written and clear, and here it is a trivial patch that add the support for the numlock key.
Since I'm not able to upload the attachment I paste it here. Feel free to tell me a better place to file bugs

--- sooperlooper-1.6.13/src/gui/keyboard_target.cpp 2005-07-29 05:19:11.000000000 +0200
+++ sooperlooper-1.6.13-my/src/gui/keyboard_target.cpp 2009-03-15 17:28:17.000000000 +0100
@@ -511,6 +511,9 @@
else if (keyname.IsSameAs (wxT("alt"), false)) {
keycode = WXK_ALT;
}
+ else if (keyname.IsSameAs (wxT("numlock"), false)) {
+ keycode = WXK_NUMLOCK;
+ }
else if ( keyname.Len() == 1 ) {
// it's a letter
keycode = keyname[0U];
@@ -660,6 +663,9 @@
case WXK_ESCAPE:
text += wxT("escape");
break;
+ case WXK_NUMLOCK:
+ text += wxT("numlock");
+ break;
default:
if ( wxIsalnum(key) )