date math in bf?

[Sean Timm]

Is it possible to do date math in a FunctionQuery?  This doesn't work, 
but I'm looking for something like:

bf=recip((NOW-updated),1,200,10) when using DisMax to get the elapsed 
time between NOW and when the document was updated (where updated is a 
Date field).

I know one can do rord(updated) instead, but I find that difficult to 
think about and the ordering may not be linear with respect to time 
making it only a rough approximation of document age.

-Sean