1) Ur-Priest:
Become an ex-druid, it's a very simple process! Just teach someone how to say "hello" in druidic and presto bingo you're no longer a druid. Or you could just forsake it. Becoming an ex-druid is hardly the most convoluted part of this build(see below). As for why? Ur-priest has a much faster spell progression, and gives access to the superior cleric spell list.
2) Sublime Chord:
Neanhoon lets you heighten powers without needing a higher level spell slot. You can heighten detect magic, which gives you the ability to cast 3rd level arcane spells.