ask him to take a look at Michael Miller's Fairy Frost line. There are nearly 100 different shades and colors of it. It's 100% cotton, but might provide the shimmer he likes. shop around, though. it's quite pricey unless you stumble across a sale. it's very hard to find for under $8.50 per yard.
this is the only site i know of that sells all the colors. you can't see the shimmer in the online pics but it's there. they even sell sets of samples.
http://www.webfabrics.net/servlet/Categories?category=Special+11%3AMichael+Miller+Fa iry+Frost
genuine silks aren't always soft and slick. you can find some that are as easy to work with as cotton. they are always expensive. i think (but don't place bets) you can even find some that are machine washable now.
if you decide to use the soft and/or slippery silks, fuse them to very lightweight innerfacing before you cut the patches. makes them very easy to work with and won't make the quilt stiff.