Frommhow I am reading it, with one of the requirements for the PRC being
"Special: Must have conjured a devil using lesser planar ally or lesser planar binding (or a similar spell) and successfully coaxed the fiend into performing a task longer than 1 day."
The earliest a Wizard could get into the RPC would be his 10th level since it too till 9 to get 5th level spells. Is there any other lower level spells that does simliar that would allow one into the prestige class earlier? This is a discussion between me and my GM, he likes the idea of my chracter in the party but we are only level 6. (Which other than that special requirement all others are met."
My thought was through a scroll, casting the spells and doing the rituals.
Just use a scroll; there's no requirement that you need to cast it out of your own spell slot.