The NetBook of Feats came up with this Feat:
SUMMONING CONCENTRATION [General: Magical]
Concentrate to maintain your summoned creatures.
Benefit: You can maintain the duration of a summon spell (such as summon monster or summon nature's ally) through concentration. As long as you concentrate on the spell, do not count time off it's duration. After you stop concentrating, the normal duration resumes and then terminates as normal. You cannot resume concentration.
SUMMONING CONCENTRATION Copyright 2001, Carl Cramér
Balance: 4.56 (Purp 5.00, Pow 3.70, Port 4.70, Comp 4.70, Rule 4.70)
~Marimmar