Hello Tony (and Steve).
Tony, the very modification you suggest has been done before by someone with a S2 or S2.2 on this forum (sadly, I don´t remember who it was). Inspired by that owner I tried this solution as well after I had terminal failure of both mounts simultaneously on my S2 . Two years after fitting the modified engine mounts function as they should, hold up well and have not caused any problems.
For EACH mount I used 6 countersunk screws ( i.e. 3 on the upside, 3 on the downside arranged in a regular 60 degree pattern ) and also added an industrial quality adhesive sealant (Innotec Adheseal) into the drilling holes before screwing the screws in. The engine mounts available today seem to be a little bit higher than the original mounts as specified by Lotus and also often lack a little "locating tab" to prevent the mounts from twisting. As a solution against twisting I added an additional little screw (NOT countersunk !) where the locating tabs should be.
Renn Ortenburger described a similar modification on his blog, which could be found here:
http://www.lotusespritrestoration.com/2010/05/preparing-lotus-esprit-s1-engine-mounts.html
I´d love to post some pictures but they sadly seem to have been lost during a computer crash .
Hope these experiences are at least of some help to you.
Greetings from Austria,
Georg
UPDATE: Found the post: