The assembler requires quite some code to be at least minimally working (i.e. to implement a somewhat working D3DXAssembleShader function).
Is it not possible to implement enough to support some small subset of the language? If it's not at all possible, then we'll just have to live with it.. but the odds of a favorable review get rather long. So if it would be possible to support the simplest shader program you can think of with some subset of the code, that would be a worthwhile approach, in my opinion.
Cheers, --Juan