I think it is possible by editing the config file
here is an exemple for the gx4000 (not for GPICASE but maybe you can try).
gx4000.videomode=CEA 19 HDMI
other mode :
for 50hz game console
hdmi_mode resolution frequency notes
17 576p 50Hz
18 576p 50Hz 16:9 aspect ratio
19 720p 50Hz
20 1080i 50Hz
21 576i 50Hz
22 576i 50Hz 16:9 aspect ratio
23 288p 50Hz
24 288p 50Hz 16:9 aspect ratio
25 576i 50Hz pixel quadrupling
26 576i 50Hz pixel quadrupling, 16:9 aspect ratio
27 288p 50Hz pixel quadrupling
28 288p 50Hz pixel quadrupling, 16:9 aspect ratio
29 576p 50Hz pixel doubling
30 576p 50Hz pixel doubling, 16:9 aspect ratio
31 1080p 50Hz
and 60 Hz
1 VGA (640x480)
2 480p 60Hz
3 480p 60Hz 16:9 aspect ratio
4 720p 60Hz
5 1080i 60Hz
6 480i 60Hz
7 480i 60Hz 16:9 aspect ratio
8 240p 60Hz
9 240p 60Hz 16:9 aspect ratio
10 480i 60Hz pixel quadrupling
11 480i 60Hz pixel quadrupling, 16:9 aspect ratio
12 240p 60Hz pixel quadrupling
13 240p 60Hz pixel quadrupling, 16:9 aspect ratio
14 480p 60Hz pixel doubling
15 480p 60Hz pixel doubling, 16:9 aspect ratio
16 1080p 60Hz