Just to resurrect this thread ..... after quite a lot of pondering and research it would appear that the answer to the above is ..... YES !
At least with Cannondale BB30 cranks as the spindles can be had seperately in various widths and they will fit road or MTB Si / Hollogram crank arms. Then there's the bearings, shields and spacers and well you get the idea !
So with some bargain road Si carbon arms and various odds and sods including a 131mm spindle which didn't work
followed by a 132mm one which did coming to and from the US and digging out various tech docs I'm finally cranked. Phew !
It did work out cheaper (seen the price of Hollowgram cranks ?
) no shims or adapters and I'm really happy with the end result.