Extending dict lookups (SQL)?

[E.B.]

Hi,

How difficult would it be to try to hack some extension to the Dovecot
dict mechanism for someone unfamiliar with the code?

I'm using SQL as a backend and am looking for, at a minimum, the
ability to specify a WHERE clause in addition to the built-in one
that feeds the current username.  The field name to test the additional
value against would be necessary as well of course.  

Naturally, full query customization would be great to have.

Perhaps providing a mechanism for the caller to pass data for
the extra WHERE clause is the hardest part, not sure... but
it can't hurt to ask.

Don't take this as lack of gratitude - I can work with what's there
and greatly appreciate it.