If you'll use system--create object instead of 'spawning' the pickups, you can use x/y instead of image point. Which will allow you to put random in the x and y parameters.
System-Create Object Pickup at
X: random(obj_spawnzone.bboxleft, ob_spawnzone.bboxright)
Y: random(obj_spawnzone.bboxtop, ob_spawnzone.bboxbottom)
add an 'player is in room' to make sure it won't do it other rooms.