Assuming you know where the netmodule is at compile time, you should be
able to tweak the csc task to add the /addmodule command line switch and
then point to your VB module.
This is assuming you are talking about a netmodule, not a VB module
file. If you are talking about a module file, then you will have to compile
it to a netmodule (you can use the command line VB compiler to do this) and
then proceed with the instructions above to integrate it into your C#
project.
However, you will not be able to reference the functions while you code
your project, which I am pretty sure is what you don't want.
If you want to integrate those functions into your C# project, then you
either have to compile it into an assembly (which I am curious why you can't
do that) or convert the code to C# and include that in your project.