Usually, if you run the executable with the "/?" switch, it will display your choices.
On old versions of SQL, it was something like this:
C:\install\SQLServer200xSPx-.exe /allinstances /quiet
You can use a network share and call it from there.
But honestly, I do not feel comfortable running service packs unattended, specially on critical servers. What if something fails? What about unexpected reboots?
Here is a useful link though: