Today, on a train ride back home from a meeting in Helsinki, osso-xterm got a shortcut key editor. So if you need a shortcut not in the default settings, upgrade to osso-xterm 0.13.mh18 and launch the editor from the edit menu.
The dialog allows you to reorder the entries and to define a label and the key(s) for the shortcut. The format for the key definitions is: "<modifier1>[<modifier2>...]KeyName"; multiple keys for single shortcuts should be separated with commas. The supported modifiers are <shift>, <lock>, <ctrl> or <control>, <alt> or <mod1>, <mod2>, <mod3>, <mod4> and <mod5>. I doubt vte does anything for most of these though, you're probably only interested in shift, ctrl and alt. The keycodes are those understood by gdk_keyval_from_name. For a list of possible values, see gdk/gdkkeysyms.h. The values accepted are those without the GDK_ -prefix.
The default settings appear in the dialog, so you may use the old definitions as examples.