If you are going to let a beholder do that, keep in mind it will be a tougher encounter for smaller parties, because one person might be wiped out in one volley of attacks. On the otherhand, it would weaken the beholder against a large group, since he is almost wasting a round by using all his eyes on one person. I feel that the eyes are designed for different opponents anyway. Fort save based ones for casters, will save based ones for fighters. They would probly do better by spreading their eyestalk attacks out to the different people all at once to try to neutralize as many people at once.
In my opinion, a beholder isnt that tough anyway, the save DC's are easy enough to pass from the attacks, hit has low HP's, a weak direct attack, easy AC, no DR, no SR, is slow etc. It also has very low saving throws itself, a monk could stun one at that level easy, and a monk should easily pass all the saving throws from the eyestalk attacks anyway.