Variable length bars

[Patrick or Cynthia Karl]

I'm trying to set a John Dowland piece (Come Ye Heavy States of Night) which 
has a single initial time signature of "4/2 2/2" followed by measures that are 
either 4 half-note beats or 2 half-note beats long, in quasi-random fashion.

It's clear that if I can get that time signature printed, I can set the piece 
by appropriate use of \set Timing.measureLength.

Can anyone point me to a way to do that?

Thanks