Deploying application addin for Word 2007 made in VS 2010 SP1 via WiX

Deploying application addin for Word 2007 made in VS 2010 SP1 via WiX

I made an addin for Word 2007 in Visual Studio 2010 SP1, and have since
hit a brick wall in terms of deployment. I would like to deploy this addin
via Active Directory and that requires MSI installer. Now MSDN and other
resources on the Internet say that in order to add the addin properly you
need to install it in Program Files (with WiX this is child's play) and
add some keys to the Registry.
In the registry among other things I need to add the location of the
Manifests of the add in. Problem lies here in that due to being developed
by Visual Studio 2010 SP1, this address can NOT be in the form of:
C:\Program Files\\MyAddin.vsto|vstolocal
but must start with: file:/// and thus must be in the form of URI, like so:
file:///C:/Program Files//MyAddin.vsto|vstolocal
So my question is, is there a macro command or something that can get me
the address of the install directory in the above form with the forward
slashes?
Failing that anybody have any ideas how do I deploy the addin short of
doing it manually by installing it by hand (and that might fail since I
need it to be installed for ALL directory users on ALL computers)?