This is called application virtualization.
The quick answer is that normal systems don't support hosting one app allowing interaction with the rest of the system by a different user.
If your friend just needs quick access to an app for a short period of time, most teleconference tools (WebEx and the like) allow sharing of only one app and allow the users to interact with that app.
If you absolutely need to set up a virtualized application while allowing interaction by yourself with the system seperately, you'll need to set up an application virtualization server.
Various Application Virtualization systems are discussed on this question: Are there any open source app virtualization solutions for Windows
A google search for "open source application virtualization" should also return some useful results.