While that would work, it would defeat the purpose of using a proxy, which is what the article was about. :p
That said, I think there is alot of added value to being able to use actual expressions rather than string literals, both from a readability stand point and from a flexibility standpoint.
This isn’t a new problem and has been solved in numerous ways in the past. The point of the article is to introduce people to proxies and how they can be used to provide other solutions to existing problems.