xinclude processing.

I'm looking at an SGML book using hundreds of entities 

<!ENTITY ex1 SYSTEM "ex1.sh">

To move this to docbook rng, I'm thinking about a script or
something to convert the callouts to xinclude statements.

1. Is this reasonable.
2. Is it only libxslt that hacks xinclude as yet?
(and any particular version please)

TIA DaveP