Manually select the last argument.

This implementation does not rely on Bash-specific functionality.
diff --git a/git-flow-feature b/git-flow-feature
index a413534..8893598 100644
--- a/git-flow-feature
+++ b/git-flow-feature
@@ -180,7 +180,7 @@
 	parse_cmdline "$@"
 
 	# read arguments into global variables
-	NAME=${!#}
+	NAME=$(last_arg "$@")
 	BRANCH=$PREFIX$NAME
 }