Actually after some digging around I found a solution that would work (I couldn't find a way to delete my post) But I guess if there is anyone looking for doing the same thing as me:
The app is donationware: X-Mouse Button Control,
http://www.highrez.co.uk/downloads/XMouseButtonControl.htm
In order to get this to work you need to create an app specific layer, if you want the desktop you create a layer for Explorer (this is what I failed to do before).
Under settings > Hotkeys, enable global hotkeys. There are the Toggle x/y axis lock hotkeys at the bottom. You can set these to any free hotkey, and what I did was use X-Mouse's 'Simulated Keys' function to bind it to a mouse button - ie: Mouse Button 4: Simulated Keys (pressed) {CTRL}{SHIFT}{Fx} *where x is the function key number
Hope this is of some use to someone!
Derek.