Some time ago IPD offered a direct replacement intermittent wiper relay that allowed variable delay. Unfortunately, the relay is no longer available, but it can still be done.
(Stop press: 10 July 2021. I just discovered that Dave Barton has a stock of the correct relays for your 240. Find them at: https://www.prancingmoose.com/240wipers.html )
Certain models of VW Golfs and maybe Passats have a relay that can be made to work. The relay you want is part number 357 955 531 with a large 99 on the top of it. (I am told that relay 3B0 955 531 with 197 on the top is a direct replacement for the 99 relay and may also work).
These relays are only fitted to higher spec cold climate cars, not your poverty pack model. I searched e-Bay and found a seller in Lithuania of all places, and they shipped me two 99 relays.
Above is the VW relay and on the bench is the original relay that I pulled out of my 262 .
The relay location is under the left foot of the left front passenger. (or under the left foot of the driver if you happen to be in a left-hand-drive country.) If you pull the carpet away from the fire wall, in the left corner of the left foot well, there is a little cavity with some wires poking down into it. The relay is simply stuffed into the hole. Grab the wires and work out the relay. It is usually taped up in foam to stop it rattling. Pull the old relay out and notice the large socket that it came out of.
The new relay will not plug into the socket of the old relay, so you have to carefully make some jumper wires.
Using male and female crimp connectors and some scraps of wire, make the following connections according to the colors of the Volvo harness:
Jump the black wire to pin 31 on the VW relay. (Ground wire).
Jump the red wire to pin I on the VW relay. (12V when wipers selected to Intermittent).
Jump the yellow wire to pin 15 on the VW relay. (12V when key on).
Jump the white/black wire to pin 53s. (Park wire)
Jump the white wire to pin 53m. (wiper motor low speed).
Jump the Blue/Yellow Wire to pin T. (washer signal).
Below is what I did. I tried to more or less match the wire colors but it is not necessary. Just be sure to get the connections right.
To test it, turn the key on and then turn the wipers to intermittent. All should operate as normal with about a 5 second default delay. Washer will give one wiper sweep.
To change the delay, wait until the wipers are sweeping and then while the wipers are in motion, turn the wipers off. When you need them on again, simply turn them to intermittent again. If you waited 3 seconds, it will remember the 3 second interval, and continue to sweep at 3 second intervals. If you waited 10 seconds to turn them back on, the delay will be 10 seconds. The maximum seems to be a bit over 20 seconds.
The key is to turn the wipers off while they are in motion, then turn them on again when you need them.
Tape it all up and stuff it back into the hole.
Have fun....
Below is a scan out of my Volvo Haynes book:
And here is a break down of the VW relay:
