Wifi Extender compatibility with mobile hotspot router

You should be able to add an extender to it. 

Another thing you can try is the fact that hotspots aren't exactly known for their wifi range because they have to be portable. 

And the MR1100 has an ethernet port. You could connect an old router/access point to it (router in access point mode). 

That'd have better range/performance (depending on what you used) versus the hotspots wifi.