configurable blueprints

[jamie campbell]

This might be a stupidly easy question or an unsolveable one.  I 
googled, checked the r4.core and r4.cmpn , and the felix and aries 
sites, wasn't able to find the answer.

I'm trying to take the next logical step with openjpa in karaf : a 
configurable datasource.  The blog sample has a blueprint file 
specifying a hard coded database name, blogDB.  I put together a bundle 
for datasource configuration management, and started writing my own 
derby bundle.  It's easy to get my derby bundle to access the common 
datasource config (databasename, host, username, password, etc), but 
.... then what?  I referenced the blog-datasource bundle, and I can't 
tell whether I'm able to write a blueprint file referencing 
configuration, like $dbname_param style, or whether I can bypass using a 
blueprint.xml and instead register the services "in code".  If I 
register them in code, I'm not sure how to translate blueprint.xml 
syntax into equivalent in-code context.registerService() calls.

I'll gladly rtfm if there's an fm to r and someone can point me at it :) 
, otherwise help is much appreciated...

-Jamie