How to add a custom intellisense to VSCode baseed on the output of a shell command?

Question

i have a shell script that extracts defined entities for a given DocBok XML document. Its output looks similar to:

&productname;
&productnameshort;
&grub;

and so on. I'd like to code an intellisense inside my extension that would be populated by pressing & and then filtered by subsequently pressed letter. By pressing &pr the intellisense list would populate the first 2 lines of the above example. Any idea?