I was able to do this with Tasker. I didn't realize that by default, Tasker will restore settings to their previous state when they exit the profile. Previously, I was trying to use a second profile to set the network mode back, and this is where I ran into problems. I also set up a second profile (along with the Secure Settings plugin) to enable/disable GPS when going between Wi-Fi.
Now, to just configure it to NOT switch the network mode while on a call.. I think there's an IF statement for that.
Phone: LG Nexus 4
ROM: ParanoidAndroid 3.99-RC2
Radio: Hybrid .33/.84
Tablet: Samsung Galaxy Tab 10.1 (wi-fi)
ROM: CyanogenMod 10.2 Diamond