Munin - Load old/historic data from a database to prepopulate the graphs?

I have a Munin setup that monitors some data from our database about the number of sales. My munin plugin extracts this data from the database with a query. I could run this query for any time in the past to see what the output would have been had I had the munin plugin then. Is there anyway to add in old data to the munin graph? Given a timestamp and some data for that timestamp, can I add it to the rrd file?

Export rrd to XML(use rrdtool dump), edit XML file. Then export XML to rdd(use rrdtool restore).

Given a bit of scripting foo, this is doable. See http://ingvar.blog.linpro.no/2008/10/21/todays-munin-tip-spooling-a-year-of-backlog-to-munin/ , and add changes according to the comment about speed.