Hmm, comfort and ktm 640 don't really go together. you get speed, ruggedness and lightness at a price:
This is what i've found the best:
engine - had it professionally balanced. ktm only have one set of weights for the 620, 640 and 660s. thats why there's such a big variation in engine smoothness - it's just luck. I have now had 6 different 640s. all different the last but one was fantastic. the first appalling - i couldn't hold me teeth together.
seat - reupholstered the pre 2003 ones. lower, wider, softer. The 2003 is fine as it is.
sheepskin (on the seat
)- a must for 2+ hours.
handlebars - fill with lead shot.
grips - hot grips enduro ones are, imho, the best. search for them lost the link.
foot pegs - standard rubberised ones.
maybe some others i cant remember - more stuff on my link.