Great question. They do have a couple of ways to 'challenge' the heart, and they would if there was no alternative and your heart is quiescent at the time of the operation. It's just better if the heart does its own talking. So, if the heart is currently cranky and showing ectopy, all they have to do is locate the general area and begin to circle that area with lesions created by RF energy. They touch the wand to the endothelium and apply energy for between 15 and 30 seconds.
Move it slightly, and repeat, and repeat until he/she feels they have made enough lesions that, when they scar over during healing in the next ten days to two weeks, it will provide a complete blockage.

The EP can use any of the following (that I am aware of): adenosine, isoproterenol, and good old caffeine. Adenosine is an inhibitory chemical that slows the heart, while the other two stimulate the heart. One, or all three, applied sequentially in whatever order is suggested, will hopefully cause ectopy.