If you allow 3.5 material, Versatile Spellcaster is exactly what you're looking for. 2 3rd into a 4th, two 8th into a 9th, (most excitingly) 2 9th into a 10th. It doesn't give any spells known above your usual, but you can use a slot above normal maximum for metamagic, or with a Runestaff or pathfinder equivalent.