Ways to Safely Repair 45 Degree Pitched Roof without Jacks?
You wear a harness attached to a rope that is thrown over the roof and tied to something solid such as a tree. 

The harness kit may look like this:



The harness is most often used in a manner as shown here. A short connecting rope goes from the middle of the high back over to a D-Clip that then attaches to the main safety rope via a Robe Grab.



Rope grabs come in various styles (one shown below) but are basically designed to permit them to slide along the rope when they are directly pushed but will clamp tightly on the rope when pull tension is applied to the connecting ring from the D-Clip and short rope to the roofer. 



This picture shows a harness in use on a roof....albeit not quite as steep as the OP has asked about.



Here is another in use application.