Thanks for the other

In reply to Opentype Random Contextual Alternates:

Thanks for the other suggestion, Nick. That alternative (@NoA) is just what I need at the moment. However, it seems like the code ends up too long:

[FATAL] (MyFont) Chain contextual lookup subtable in GSUB feature 'calt' causes offset overflow.

Any thoughts, anyone? Any trick to make it work? Many, many thanks in advance.