I am planning a job where the customer has already purchased vertical steel siding, which is fastened 12"oc. And although I would use BuildBlock, which has webs 6", with common seams and corners I doubt it will work out to install directly on the ICFs.
Any ideas? I would rather not use horizontal wood furring strips, what choice do we have?

Brad,
Some type of horizontal stripping is necessary for vertical siding installation.
Other than wood, I only know of two options--metal or composite. Both of these will be
very expensive when installed 12" oc. If your worry is wood deterioration, you might consider substitiuting a PVC trim piece in lieu of wood 1x's. These should be readily available at Lowes', etc. Not going to be cheap, but will probably last the life of the house.

Wes, is it a solid material, or an angle? In Fold-Form's instructions they say to embed a plastic angle to attach siding, Fold-Form does not have continues ties/webs.

What about galvanized "hat track". I think it is cheap, but it might have a profile larger than 3/4".

Brad,
The specific PVC piece I was thinking about is about 3/4" x 2" solid. In essence, it is a replacement for 1x2 wood. It is used a lot around here for triming out garage doors, etc.
My thoughts on metal would be either a 'hat' or a 'zee', however, I don't know if either one would be available small enough not to create problems with window/door trim, etc.
The company that makes 'roof huggers' were working on a zee with perforations in the leg for use under metal roofing. That would be ideal if it is not too large. However, I don't know if it ever made to market.