Storing code in library/dll

I have some code which I would like to allow third parties to implement (but not have access to the code).

(I believe) this is straight forward enough for non-template classes (as I would just supply them with a set of header files for the definitions along with the dll containing the actual class/method implementations)... but how would that work with template classes?

Based on this article, I can seperate the code from the definitions (using Chris A's answer regarding .hxx files)... c++ template and header files

This means I can have a series of header files that contain only the definitions of my template classes, but... how do I put the implementations in a dll?

If I know what template parameters will be used, I am presuming I can get my dll to compile with the appropriate classes in it, somehow.

If I don't know what template parameters will be used, I am presuming I can't and therefore can't avoid giving access to the class implementations.

Can anyone please give me some input on how I should approach this?

I am using qt dynamic linked libraries.

Thanks!