AFAIK, Inkscape calls an executable called perl.exe without any parameter. It IS possible to modify this under Unices via a preference.xml file, but this file does not exist in the windows version and I do not have access to the process environment to setup a variable at startup.

The Inkscape documentation for extensions contains a procedure for setting up paths to interpreters which tells how to find where the file is:

2.Open your perferences.xml file with a text editor (find the exact location of the file by going to Edit -> Preferences -> System: User Preferences)

The procedure mentions Windows so it leads me to believe this will work on Windows:

4.Insert a key for the interpreter, for example 'python-interpreter' for setting the program that should be used to run python extensions, and set the string to the absolute path to the python binary which is compatible with Inkscape's current extension scripts (in the example below, the path is "/usr/bin/python2.7". It will look different on Windows systems.):

In case there is already a version of Perl on the system you could follow the approach that the portable version of Strawberry Perl uses with the portableshell.bat file. Instead of calling a Perl executable file directly you can call the bat file and it sets up a temporary environment with the Strawberry Perl folders at the beginning of the path and then runs perl.exe. This means the modules that are installed with Portable Perl are used instead of the ones installed in the system Perl.