Whoh. I didn't even look at how cleric spell casting works until now, but now I see clerics cast spells Pseudo spontaneously. Um, unless I'm missing something, since clerics don't have any level based limit on spellcasting, which is the limitation on multiclassing, a one level cleric dip when you are any spellcasting class basically adds the whole clerics spell list to your own. (Although, only a couple of spells from it per day). Although this presumably has a lot of implications, for a necromancer at least it means they take a one level dip in cleric, then prepare animate undead as a cleric spell (along with other spells of the same level you plan on casting it as), cast it, then use arcane restoration to gain back the spent spell slots and recast them as you want or need too as the other cleric spells you prepared.
Of course, that whole process sorta hinges on the fact that although multiclassing spellcasters are clearly suppose to be limited in their access to spells of higher levels (as clearly demonstrated by their examples) in all cases the actual knowledge of spells you get and what spells you can prepare is determined by what spell slots you have, which multiclassing doesn't effect.
Thinking about it, clerics (or any spellcaster) themselves could also just take a level in wizard for the same effect, although they could only get free spells of the level that they dipped in, as they level up they can just write higher level spells in their books and then prepare them as normal. Although for necromancers specifically they need that arcane restoration so wizard gota be the main class. But in theory something like, wizard 1 cleric 1 druid 1 (druid spellcasting working the same way as cleric) bardorsorcerer x All cleric spells, all wizard spells, all druid spells, all bardorsorcerer spells. (Might not actually be worth it, considering stat points and loss of class features, but the idea is there.)
Of course, I might be missing something here. And clearly it's not quite what the rules intend. But, it's interesting.