Are you wanting to help them through the summer or are you looking for an all season boost? If you are just wanting to plant something for the summer then I would go with Lab Lab (assuming your plot is an acre or larger) or I would plant a plot of late soybeans. I did the Lab Lab last year and they loved it. This year I'm going to switch it up a little bit and plant soybeans sometime in early June whenever I catch a good soaking rain. This way the beans I planted should still be lush and green come the first part of bow season when all the other soybean fields have started to wilt and die.
If you want to plant a perennial I would concentrate on getting the pH to 6.5-7 and make sure all the weeds are killed and plant clover in the late summer. This way the young clover plants don't have to suffer through summer droughts. They can have the fall rains and get established when weeds or starting to die. This way they have a jump start on what weeds are left come spring green up.