So, I discovered something interesting, a Spellstitched Necropolitan can qualify for Malconvoker at Level 1, like this
[spoiler=SpellStitched Necropolitan Demon Summoner]
Referencing Complete Arcane page 72, under
Specific Spell Requirements, we learn that Spell Like abilities can qualify you Prestige Classes and Feats that have the wording of "Ability to cast XXXX." So with 16 wisdom you get two 3rd level spell likes per day, which you make Summon Monster III. There, you qualify, the only problem is the following:
- The Ritual of Crucimigration (Libris Mortis page 115) costs 3,000 gold.
- Spell Stitching (Complete Arcane page 161) costs 1,000g, and 500 XP x Wisdom, bringing the cost of spell stitching to 41,000gp (16x500x5+1000).
- You should only have about 2,700gp at level 3.
So to do this you would either have to find some adamantine doors to sell, or start off at level 10 and spend most of your 49,000gp on it and be poor for a long time. You have to be a Sorcerer, and a race that has an extra feat so you can get Bluff 4, Knowledge (The Planes) 4, Spell Focus (Conjuration), and Augment Summoning. Malconvoker requires you to be non evil, which is lucky since Necropolitan doesn't force you to be evil (the example necropolitan is neutral).
Spellstitched Necropolitan
Lvl01 Sorcerer 01
Lvl02 Malconvoker 01
Lvl03 Malconvoker 02
Lvl04 Malconvoker 03
Lvl05 Malconvoker 04
Lvl06 Malconvoker 05
Lvl07 Malconvoker 06
Lvl08 Malconvoker 07
Lvl09 Malconvoker 08
Lvl10 Malconvoker 09
Lvl11 Fiendbinder 01
Lvl12 Fiendbinder 02
Lvl13 Fiendbinder 03
Lvl14 Fiendbinder 04
Lvl15 Fiendbinder 05
Lvl16 Fiendbinder 06
Lvl17 Fiendbinder 07
Lvl18 Fiendbinder 08
Lvl19 Fiendbinder 09
Lvl20 Fiendbinder 10
[/spoiler]