"Is there anything I can do (besides a transmission rebuild) to minimize this clunk?"

Yes, I think so.
I had a similar problem. I have tried "Lucas Transmission Fix" and it works great. I felt the difference immediately (back to normal: very smooth like new).

Recently, I have found through website search and my co-workers that a lot of car deals add these kind of additives including “BG-44K transmission treatment” to keep the valve body clean after replacing (or flushing using a machine) transmission fluid for their customers’ cars/trucks.

When I had this transmission problem, I thought I had only two choices: one is to get it fixed (my 88 240 is only worth $1600) and the other is to give it away and buy a new CAMRY. But I said to myself "How come? Most people say that Volve lasts very long" and my transmission just lasted for 12K miles. There must be something that I do not know.

I went to Autozone and they recommended me "Lucas Transmission Fix" ($7.99). Initially, I did not expect that this product could solve my problem and I already made up my mind if this product won’t work, then I would buy a new CAMRY, not Volvo any more (I like real Volvo, not Ford).

And now, my transmission works great!! I will keep my Volve until it reaches 20 or 30K miles.

What I have learned this time is to add Transmission Additives each time when flushing or replace transmission fluid.

Good luck.

Note: Transmission additives work only when transmission is not shot.