Did your coach specify why s/he was against training that way? I am a fairly strong runner and when I asked him about it since I noticed all the runs were that pattern, he said he wanted me to get used to it, so it wouldn't be new for the race. If its something you want to do, I would try it and see how it feels.

I volunteers on the run last year at LP and the majority of people where walking the aid stations (or more).

When is your IM?