Aside from patron spells, are there any ways for a witch to get spells from the wizard/sorcerer spell list? Items, feats, class options? The biggest weakness of the witch spell list IMO is the lack of defensive spells, so being able to get spells like mirror images, displacement, stone skin, and others would be useful.
A spontaneous witch - there's at least one, the ley line archetype - can use a ring of spell knowledge to get off-list spells.
The pathfinder savant/arcane savant PrC can get off-list spells. It loses a caster level and doesn't advance hexes though.
There's a wizard archetype which can use shaman hexes, the spirit whisperer, which could be a different solution to your dilemma.