install[i]=- will work for .uninstall rules.

build.zsh.in

@@ -314,6 +314,10 @@ function main {
 			write
 		fi
 
+		if [[ "${installdir}" == "-" ]]; then
+			write "${target}.uninstall:"
+			write ""
+		else
 			if exists "${type[$target]}.uninstall"; then
 				${type[$target]}.uninstall
 			else
@@ -322,6 +326,7 @@ function main {
 				write "\t${Q}rm -f '\$(DESTDIR)${installdir}/${target}'"
 				write
 			fi
+		fi
 
 		if exists "${type[$target]}.test"; then
 			${type[$target]}.test