You can do this today if you have the product Payroll Extensions installed or on Microsoft Dynamics GP 2010 install it is called Human Resources and Payroll Suite.

In this product there is an add-on for Payroll called Payroll Integration to Payables (PIP).  Once you set this up (very easy and free to all payroll customers) then you can link a deduction or benefit to a vendor.
Once you post payroll, the vendor record will be updated with this amount automatically.  You can link a vendor company-wide or employee specific.  You can also link up taxes too, really COOL!

If your company is not using PIP, you should check it out, the product will save your company time and money, now who would not want that?

Attached is documentation too!

Thanks
Terry