It's not really meant for that, but you can go around the intended use. You can create a drone like pad (e.g. by adding effects to pads or strings) and then give it the longest delay time and max out feedback so it becomes self oscillating. It will get quickly incrementally louder this way though when using the analog delay setting. You need to find the perfect depth amount to keep it from fading or becoming too loud.

Another option is to use a (latching) sustain pedal and turn the sustain pedal off for other sections (if you wish to play other sections while the drone is playing) and hold sustain indefinitely. The pad samples don't fade while sustain is on (at least it takes time if they do). Then after initiating the drone sound with sustain on, you can turn off the section (Edit: You can't) and turn on other sections, and it keeps on playing and you can use the keyboard to play something else if you wish.

Edit: After testing it out, I realized that you can't turn off the section, as the sound stops immediately. However, you can set the drone to low split and others to high split and after you play the drone sound, change the split point to lowest key on the keyboard. This way the same sound keeps playing, but doensn't affect your playing.

Also, if you wish to alter the drone pitch, you can turn off pitch bending for other sections and bend the drone pitch with the pitch bend stick (you can set how much you want it to change). Alternatively, if you want to use pitch bend stick for other sections, that are not part of the drone, disable pitch bend for the drone sections.