update
So first, I know this is my problem. I only mentioned that I'd for it not to be my problem.
Next, sure, a RIP can convert rgb to cmyk, but as someone else said, it cant do neon, it cant magically bend the laws of physics. If this was just a slightly out of gamut image, I could have lowered expectations, but they specified they wanted retinal shock neon. So, spot colors it is.
I did find a site that would cost a lot more, but would do screenprint spot colors (neon green and purple, etc). I looked up the retail price and sent that to the client. Told him to have his daughter pick the insane colors she wanted, that way she would get what she asked for. Are the colors tacky? sure. but its a kids product made by a kid.
BTW, to the person who suggested Stouse, THANK YOU. I went there, noticed the ink colors they offered matched the retailer I found previously to a tee. Did some research and turns out the retailer outsources to Stouse. So now I can charge slightly less than the retailer, and make a nice little profit.
As for SVG, it was a bit of a pain to put all the shapes together so it was clean layers, but only a few minutes of griping later and I was done. In the end, clients daughter will get the colors she wants (taste be damned), client is already willing to pay for a 4 spot color job, and I came out making a decent profit for the headache the designer induced.
Thank you all for your input, I appreciated the groupthink on this.