Installing nonfree packages on Parabola

I've got an install of parabola running on a virtual machine, and I'd like to install the [virtualbox-guest-utils package](https://archlinux.org/packages/extra/x86_64/virtualbox-guest-utils/) . Unfortunately it's in the Arch [extra] repo, and Parabola already has an [extra] repo. Is there any way to rig up pacman so that it will search the Arch repos after failing to find a package in the parabola repos? I was thinking that maybe I could maintain my local cache AND db file under a different name like [arch-extra], but I can't find any information on doing that.