Non translatable content in Docbook 4.x

Dear All,

I'd like to mark some text as non translatable. I could add a common
attribute to all elements in original DTDs, but I like the idea of utilizing
ITS standard for this purpose, which seems to be supported in CAT tools.

I've found this explanatory article, but I'd like to use it in old 4.x DTD.
http://xmlguru.cz/2013/05/docbook-and-its2

Is there any way? Some extension like for xi:includes ?

Btw, there is no ROI to switch to Docbook 5.

Thanks, Jan