If you can warm it up one degree during installation (maybe leave the door open?) you can use one of Beldon's DataTuff Enhanced Category 5e cables.
Operating Temperature Range: -40°C To +75°C
Storage Temperature Range: -40°C To +85°C
Installation Temperature Range: -25°C To +75°C
They have a whole list of different versions so you should probably contact them directly or search the site yourself:
http://www.belden.com/Then click on The Beldon Catalog,then Industrial, then Industrial Ethernet then Data Tuff. I think every Data Tuff cable has about the same thermal range tho some of them have a note that says they get derated by length.
Europe
E-mail address:
sales.info@belden-europe.comThe Netherlands (European Headquarters)
BWC - The Netherlands
Edisonstraat 9, Postbus 9
5928 PG Venlo, 5900 AA
The Netherlands
(Contact the number below to obtain the distributor nearest you.)
Phone 31-77-387-8555
Fax 31 77 387