diff -urN coreutils/PKGBUILD coreutils_prefixed/PKGBUILD
--- coreutils/PKGBUILD	2015-02-28 11:40:26.205559513 +0100
+++ coreutils_prefixed/PKGBUILD	2015-02-28 11:41:44.479080115 +0100
@@ -26,8 +26,8 @@
 build() {
   cd $pkgname-$pkgver
   ./configure \
-      --prefix=/usr \
-      --libexecdir=/usr/lib \
+      --prefix="${prefix:-/usr}" \
+      --libexecdir="${prefix:-/usr}/lib" \
       --with-openssl \
       --enable-no-install-program=groups,hostname,kill,uptime
   make