You have to understand how Maven uses the POM. It has a "Super" POM which defines a lot of defaults which it loads into a internal object model. It loads your POM on top of that. When the Help plugin generates the effective POM, essentially it reads the object model and creates a POM based on that. But what you want if the POM to be read as a text file with certain properties filtered. The only two options are I think of is to use the Versions plugin (which I already mentioned) or the Resources plugin (have it copy the POM filtering the properties), but even that will filter more than what you want. The only other option is to write your own plugin to do this (that's what we did, it's not that hard and you end up learning a lot about how Maven works in the process).
By the way, I haven't mentioned this yet, but placing properties in <version> will cause Maven 3.0.x to complain - a future version of Maven could disallow doing this. Our plugin gets around this by using a keyword within the version
string (just like you can use the keyword SNAPSHOT), then Maven is happy.