Both the official FLIR app and Georg's won't install from the Play store saying that it's not supported. Yes, it's the 2012 Nexus 7. Now that I think about it, it probably wants a rear camera for the live image blending. I'd rather have the option to use it with only the thermal image.
I don't think it required Rear Camera, it's not used (except when available for white led lighting, but I don't think it's "a requirement/condition").
Do you have any Android device that it will install on? You can install it to another device and extract the APK to install it on the 2012 N7.
I've done that for Flir Tools, installed on my Nexus 4, get the Apk and transferred it on low-cost Amazon Fire 7.
On the opposite I've installed Flir One Official App on the Amazon fire 7 and get the apk, installed it on the Nexus 4... it's not working because OTG is not activated in the Kernel (hardware available, but without power on the USB port, so need to root / change ROM to get part-OTG support, which is sufficient for Flir One since it has it very own battery).
One other possibility, does the FLIR require USB OTG? If so, it won't work on the 2012 N7 at all because it does not support USB OTG, while the 2013 N7 does, so that would explain why it works there.
Flir One and App from George require usb OTG. As far as I read OTG support for Nexus 7 2012 is fluctuating, some version of Android doesn't support it, some need configuration, and some work directly. I suggest you dig about Nexus 7 2012 OTG / storage / ethernet USB / media importers, you may or may not need to root it / replace the ROM by a newer Android version (at your own risk).
If you are not ready to take risk (if needed), you could find a phone with a faulty SIM (someone did so with Motorola for something like 30$, maybe Fraser) or you could take a low-cost tablet such as Amazon Fire 7 (need a bit tweaking but works like a charm without root or ROM flash - I've written a post on my experience).