[Remind-Fans] every monday within a date range

[Rupert Levene]

How can I specify 'every monday between 20 January and 5 March'? At
the moment I'm using 

SET period_start 	'2004/20/1'
SET period_end		'2004/3/5'

if today() >= period_start && today() <= period_end
	Mon		MSG week [(today()-period_start)/7 + 1]
endif

but this means I have to specify the period boundaries explicitly
rather than in words. I was hoping for a one-liner, but I can't see
how to do this.

Rupert