while it might not be practical. .
I don't even know if the suns light produces a noticable effect or not. . . are the orbital calculation for them any different than for an astroid? in any case if it wasn't negigible then perhaps you could instead shield the sun from the comet. . . you could nullify the suns effects and over a long time it will have retain enough energy to wix by the earth ahead of time and nt hit it. . . .
of course this would have to be BIG and you'd have a heck of a time trying to keep it in front of the comet. . . in fact I think the size of such a shield would be extremely prohibitive.
-Justin Kelly