Extending the cable itself is easy. All that would take is an RJ45 coupler and another length of patch cable. The problem is that you are dealing with DC current, which is going to drop in voltage the further you push it.
The fixes would be either to raise the PoE output voltage (which there is no provision for), or move the PoE power supply closer to the camera. The latter isn't impossible, but it might be more trouble than it is worth. You would need to isolate the power feed from the NVR, and then add in a PoE power injector of the appropriate output closer to the camera.
If you are going to go with wireless, try using a phone or tablet near the location where you will place the camera. The camera has a better WiFi antenna than a typical mobile device, but if you can't get a signal at all, you'll likely have issues with the camera unless you take further measures (i.e., higher gain antenna on the camera or direction antenna from the wireless access point).