Spontaneous Mystic Theurge Help

[Catarang]

Hi guys!

I'm currently about to get into a lower level pathfinder game with some friends, and I was hoping to play a Mystic Theurge. I have already asked the DM to house rule in 3.5 Sorcerer 0th level spell progression and the 3.5 class Favored Soul. However I'm having trouble with selling him on allowing, even with a house rule, Mystic Theurges to spontaneously use Combined Spells, since the ability specifically does not allow this. Could anyone point me to a better way to get arcane and divine casting progression for spontaneous casters from 3.X, preferably one that doesn't require me to be a bard, or a way to get combined spells spontaneously from a feat or some other source?
Thanks upfront.

It probably doesn't matter, but my current build is as follows:

Human Sorc/Favored Soul/Mystic Theurge

Sorc 1 Versatile Spellcaster, Heighten spell
Sorc 2
Favored Soul 1 Practiced Spellcaster (Sorceror)
Mystic Theurge 1
Mystic Theurge 2 Maximized Spell

[golem1972]

At 14th level, you are going to be Favored Soul 12 / Sorcerer 12 when you max out your Mystic Theurge levels. What are your plans after that? More base class levels or Prestige class levels that advance one side of your casting? You could max out at 12 / 18, or split for 15 / 15.

OR

Since you are using early entry cheese anyway, you may not mind a tiny bit more cheese. Joining a magical academy and gaining enough prestige in it can grant you a bonus spell casting level. Not just a caster level, a whole spell casting level with extra spells and higher level spells as if you had taken another class level. More prestige will bump that to +3 levels and +1 level in a second spell casting class. So, at level 4 instead of Divine 2 / Arcane 2, you could be Divine 4 (3+1) / Arcane 4 (1+3). At 14th level, when you max Mystic Theurge, you would be 14/14 instead of 12/12.

AND, a little more cheese could see you adding in the Deific Obedience feat (an ok feat on it's own) so you can take levels in Evangelist. Evangelist gives you 9/10 advancement of another classes features. So, Oracle 3 / Sorcerer 1 (4/4) / Mystic Theurge 1 (5/5) / Evangelist 10 (14/14) / Mystic Theurge +5 (19/19). 9th levels spells on both sides, and a lot of class features. Your bloodlines, mysteries, and curse won't advance much though.