That is a good cheap, do it yourself modification.  I have an infinitely
adjustable programmable intermittent relay on my van that is an off the
shelf item.  I bought it years ago, I think to put it on my '79
Scirocco.  Plugs right into the stock relay location and requires no
additional controls.  It is adjustable from about 1 second to about 40
seconds.  To set the time you take the wiper stalk from off to int, then
back to off.  wait for the delay you want, then back to int, and it repeats
that interval.  I assume these are still available?  It was about $30 US
back then...

Edward