I would go ahead and price the COBRA and offer those other services - if it is as expensive and complicated as it appears to be, no one is actually going to elect the COBRA. Carve these services out of the general medical plan (as you have apparently done) and let former employees choose, or not, the coverage.
If that is untenable, as you note, the rules are pretty old and there is no enforcement activity around them. Since the services seem to be for testing and the like, failure to offer them is likely to be a small risk. The larger risk is the penalty for not offering COBRA at all.