Absolute URL without scheme prefix

I'm thinking about making my site accessible over http as well as https. One thing I noticed is the absolute URL requires a prefix. I tried changing it from "http://" to just "//" (so it uses the same scheme as the page) and it fails:

java.net.MalformedURLException: no protocol: //localhost:8080
	at java.net.URL.<init>(URL.java:585)
	at java.net.URL.<init>(URL.java:482)
	at java.net.URL.<init>(URL.java:431)
	at org.apache.roller.weblogger.ui.rendering.velocity.deprecated.ContextLoader.loadPathValues(ContextLoader.java:420)
	at org.apache.roller.weblogger.ui.rendering.velocity.deprecated.ContextLoader.setupContext(ContextLoader.java:192)
	at org.apache.roller.weblogger.ui.rendering.model.ModelLoader.loadOldModels(ModelLoader.java:57)
	at org.apache.roller.weblogger.ui.rendering.servlets.PageServlet.doGet(PageServlet.java:436)

Is it possible to enhance the "$absBaseURL" macro to allow no prefix? 

I'm using Roller 5.0.3 on Tomcat 7.

Thanks,

Matt