You're frustrations around the limited options within Device Relocation rules are certainly valid and the workaround you've developed is basically the same process that we leverage, outside of creating a unique Staging folder for each device model. I don't believe you can actually write to an INI file via a SOTI script in Android (hopefully I'm wrong) so you may have to create a unique INI for each of your device models that has a "hardcoded" model name value and then use a Profile with Filter Criteria of Model for each device. It is certainly frustrating that Model, Manufacturer, and OEM Version are all options Filter Criteria but not options for Device Relocation rules. This approach would be a little less dynamic than ideally writing the macro %MODEL% value to the file automatically through a File Sync rule but it would work. 

One other approach that I've leveraged is utilizing the OEM Version and/or LG Version extracted from GetPatchVer as the CustomData for inferring the device model. Its a little trickier keeping track of and maintaining than a straightforward device model but the OEMVersions across those device models should hopefully be unique. That probably won't be the case with all of the next generation SD660 devices that will share common OEM Versions and LifeGuard updates like the Atlas (TC51, TC70x, MC3300, VC80x) devices do today.