The reason there is not enough there for Penal Substitution is that the theory makes too many assumptions that are not in the Bible.I agree. Now, I'm not going to demand that you name this as I do but to me, there is no logical leap in saying that Jesus taking upon Himself the wages of sin for us is substitutionary in the sense that for me as an individual, he was taking upon Himself the wages of my sin too.
Now, like you said earlier, I don't believe either that Jesus was made literally evil, but what he took upon himself was the wages of sin and like you said "for us". In Acts 10:43 it is said that whoever believes in Him can have remission of sins. I think there are plenty of verses that tie in the believing in Jesus and getting sins remitted. Now, could he do this without the cross? We can again go to scripture and there are verses bringing out the connection between God's willing to be just in doing all this and it is explicitly stated in Romans 3:21-26 that this occurs because of the work of Jesus as a propitiation.
Personally, I think there is enough right there for the term penal substitution. If you are willing to let "propitiation" mean propitiation in the passage from Romans above the argument is over, in my opinion.
I just want to say that the scripture is there but it's there for each step. I think that is a perfectly legitimate method when forming a theological concept.
First, the wages of sin. Penal Substitution Theory assumed that this is God's wrath inflicted as punishment for sins and that this wrath was inflicted on Christ instead of us as a means to keep from punishing us (it is not true forgiveness, but a transference of punishment).
The wages of sin are the wages of sin (not of God). Sin produces death, plain and simple. The Judgment is a Christ-centered event (all judgment has been given to Him) when God's wrath is poured out on the wicked.
In the Bible these are two distinct things - the wages of sin (not of God) and the judgment of God.
The word "propitiation" means a sacrifice or offering by which one avoids wrath or some undesirable event.