Long prints shifting with Ultimaker 2
If the brim is firmly connected to the part and sufficiently large, you could "duck tape" the brim to the bed after a few hours; by then you should have enough space/clearance to work with. 

But maybe the best advice is to invest in a heated bed platform, or use the heated bed if you only did not enable it. Heating the filament to the point close to the glass transition temperature ensures that the printed filament stays ductile. Once filament cools down, it shrinks and cannot grip on the to build plate indefinitely.

My Ultimaker 3 uses a heated build platform that can virtually make every filament stick to it as long as you prepare the bed correctly. On glass I prefer to use a specifically designed printing spray called 3DLAC; that, and a little heat (depending on the filament you print; i.e. the glass transition temperature) make that I never have had any problems with getting filament to stick to the build plate. I'm even able to get the slippery filament POM to stick to the heated bed.