Rear shock(s) preload adjustment w/out special tool

How can I compress the rear shock spring on my 83 CR in order to increase spring pre-load without a special tool to compress the spring?
I need to move the top collar(s) lower.

I used a clamping tool purchased at a local hardware to compress the springs on my 78 OR. In the first two photos, you can see how I looped a poly cinch strap through the spring. One side of the clamping tool hooks into this loop. The other side of the clamp was placed on the end of the swing arm. A few squeezes later, the spring pulls away from the upper collar and you can move the ring to a new groove. Hit the clamp release and it will spring back into place. Watch your fingers.

Now ya' see, that's why cafehusky is the best!!...I'm not kidding you -- you folks are knowledgeable, but more importantly -- extremely resourceful. I've learned more DIY and backyard/shade tree tips, tricks, and how tos from this site than I ever have anywhere else.

LtCol -- hope you can make it to Budds Creek this weekend...Should be a good start to the vintage race season...I won't be racing Saturday -- I've got contractors that will be at my house that morning, but I'll be at Budds in the early AM to deliver and pick up a bike to the track that day. If all goes well with the house on Saturday, I'll be back at Budds on Sunday to race.

AWESOME Long Range you are THE MAN!
Now I can get the boingers tuned for 2 days of racing at Budds Creek.
Skoalman, will see you there. I am doing both days.
83 CR 250 #32A Blue Doge Pickup. I usually try to park near sign up area.

Long Range's tip worked well. Could only compress spring far enough to lower 1 notch at a time but got it done. Due to the angle of the 83 shock I anchored one end of the clamp at the bottom of the shock

LtColMXUSMC131,
Glad that method worked for you. Have fun at the races.
LR