Previously, there were someone flashed the C6606 FTF file to have their c6603 (Z) working under 2600 in Canada. I guess it would work for Z1 as well (Some CPU both C6903 and C6906) and searched on xda. Only saw some people talked about it, but no one tried it.
Therefore, I gave a try this afternoon and it works. My Z1 is running under LTE at home now. According to the Speedtest, LTE is 4 times faster than H+. lol
1. Download same version of C6906's FTF as your cellphone from http://forum.xda-developers.com/show....php?t=2469191
In my case, my C6603 is 14.3.A.0.757, so download C6906 14.3.A.0.757 Generic CA 1276-7484_R4C.
2. Flash it with flashtool and bandbase only.
3. Reboot. You will find your LTE is working if have the lte signal.