Here is a pic of a metering block. I tried to show the liquid line restricted. You can see a non restricted line on the other side of the block. The pencil is pointing to the restricted line. I used a an 0.018" steel wire and bend it in a "U" shape so that it fits in both ports. It is retained by the metering block flat gasket.
I get the wire from just about any parts tag, they all seem to use this wire and are readily available in most shops. If you can change a powervalve, you can do this mod.
This shows the wire installed in the two holes the pencil is pointing to as well as another similar wire not installed.