How to heat up a Printrbot's hotend using an SD card
Sure there is. As you use Cura, you can grab any G-code file (you already have) and use it to set hotend temperature (delete the actual printing part from the file) to get something like this:

;FLAVOR:Marlin
;TIME:102
;Filament used: 0.0573674m
;Layer height: 0.2
;Generated with Cura_SteamEngine 3.3.1
; M190 S60 ;-&gt; this sets the bed temperature so we can comment it out
; the next line sets the hotend to 200 degrees Celsius
M104 S200


As every line that starts with a semi-colon is a comment and is ignored by the printer, M104 S200, would be the only line you need in the printout file.

If you're interested in knowing more - look here: G-codes on reprap wiki