How to drive a client-side application from within a task

[andrewlove]

I have a requirement that states:

When the workflow process reaches the task "Send letter to the client", the user should claim the task and and at that point the task action should launch MS Word and open up the client letter template document ready for the user to typr into.

I was thinking along the lines of the task executing client-side javascript or some other form of scripting.
Imagine for example if our .NET app used the Activiti REST API to claim the task and then (this is where my knowledge of Activiti tends to zero) retrieved a lump of action Javascript from the task "body" and executed it client-side.

Is this at all possible in any shape or form? 

Many thanks

[ronald_van_kuij]

why should it retrieve a lump of javascript and not just open the template? E.g .based on a variable set on the task that can be retrieved from the taskService? I would never trust a client to execute javascript send from the server NOT in a sandbox