I confess that minor mods on CofA aircraft isn't my strong point, but I'm pretty sure there's a standard application form.
I'd suggest giving the regional office a call (the numbers are all in CAP455 somewhere), ask to speak to a design surveyor, explain what you want to do, and with any luck they'll send you the paperwork you need and explain any significant points.
But, my instinct is that drawings, the FAA documentation, a few sums showing that the CG change is so small as to be insignificant, the CAA's own form, and the all-important cheque, will probably do it.
A couple of steers for you; do make sure that the attachment to the strut is either clamped on the outside or picks up on an existing bolt, don't drill anything - that's sure to cause problems. Don't run any cable near a wing leading edge, and make sure if it's running from the aircraft power supply (if you've got one!) that it's independently fused at about 50% above the maximum rated current. These are the standard sort of things that they'll look for.
Cheers,
G