Load a local file from a website request - available options?

I've a hosted .Net MVC HTTPS website that my customers use. I want to be able to open files (i have the full local paths to these) on their local infrastructure from my wesbite request. I realize there are security issues here and that is why browsers dont allow this.

However I'm unsure what options are available to me to get this to work. If required they would allow me to install some service\application on local PCs to get this to work.

I realise the question is fairly open but I'd like to know what my options are here? What software (preferably open source ) would be available to make this work? If possible the solutions should be browser agnostic.