Paying for Metamagic with spell slots?

[SinsI]

Is there any feat or ability that would allow you to spend a different spell slot to pay for Metamagic, instead of casting the spell from increased spell slot?
If there are none, how powerful would such an ability be? What limitations would be good?

[sideswipe]

illumians can do this as one of their sigil combinations, as well as having Divine meta magic for any metamagic as another combination. there are a couple of others that do similar effects as well.

[SinsI]

illumians can do this as one of their sigil combinations, as well as having Divine meta magic for any metamagic as another combination
Naenaesh is only for Still spell (and not really paying - one spell slot makes all spells of the same level Still for free), and Naenhoon pays with turn attempts, not with spell slots.

[The Insaniac]

The Ultimate Magus' augmented casting ability lets you do this. You sacrifice a slot from one of your classes to apply metamagic to your other class.

[Doc_Maynot]

IIRC Ultimate Magus lets you do that a limited number of times per day

[SinsI]

Thanks. Weird requirements, but just what I wanted.

[Biffoniacus_Furiou]

Thanks. Weird requirements, but just what I wanted.

Be sure to combine Beguiler with Wizard so you only have one casting stat. I've posted quite a bit before (http://www.giantitp.com/forums/showthread.php?296176-Ultimate-Magus-Is-it-any-good#4) about this type of build.

[Troacctid]

Versatile Spellcaster works on metamagic. So, for example, you could use two 2nd-level spell slots to cast one 2nd-level spell altered by a +1 metamagic.