shorter and less frequent ??
I hope by that you mean because they are going so super freaking heavy they need extra time to recover and/or 'cause they will be eating instead

.
I am a dedicated ectomorph (have been practising for almost 22 years now

) and I dunno that I train any differently from anyone else. I go as heavy as I can for 6 or so reps, use sets of 2 (will soon be 3 or 4) per exercise, 2 or 3 exercises per muscle group and do each muscle group once a week.
in between time I eat lots and lots and lots (I don't care what, if it healthy all the better, if it's not ... ah well it is still calories

)
I also don't dedicate any time to a 'cardio specific' routine (though I would not say I am unfit

).
I think an ecto should approach their
weight training like anone else trying to gain mass.
EDIT: dagnammit how did you beat me to that one 3 lol! I'm going to sleep.