I am using Intel RCS with a GoDaddy Certificate. Productively i had to use an AD-Account, but in the lab environment i started out with the network service account too. I can't say wheter you can install the .p7b-Certificate with RCSutils.exe, but you can start mmc.exe as Administrator, add the snap-in for Certificates for the computer-account and can there manually import (or export) everything that you need. You will find the certificates installed by RCSutils for the network service account there too.
The active certificate is stored under personal. I had to add the root certificate for my test-CA under Trusted Root Certification Authorities, but the root certificate for GoDaddy was already installed.
Effectively, on our Windows OS on the server, the root certificate was present by default, so we only needed to add the PFX certificate.