That would require having pull aircraft out of service for extended periods for modification; putting in a modified fuel tank probably takes lesser time and needs lesser rewiring.
OTOH, the Super Hornet international roadmap concept does have an integrated IRST below the nose.
http://cdn-www.airliners.net/aviation-photos/middle/5/4/8/1866845.jpg
Not all that long. You'd do it during a regularly scheduled depot maintaince period. Or maybe even during other scheduled maintaince at the unit level. Modern units would have smaller electronics "boxes", but the actual sensor head would be about the same size. Those were as I said, in a fairing just under the windscreen. You're probably correct about the wiring though. The center-line station is likely already wired. The IRST is not an imaging sensor, so only control, power and aircraft "state" information (pitch roll yaw, and maybe angular rates) need be supplied, while the output would just be "hits", which would be pretty low bandwidth compared to a video signal, and would likely be accommodated on the existing digital data bus, except for the power.
