I'm not aware of any feature that ensures you don't you stockpile excess stored goods in that context. Maybe you can destroy some factories to reduce social production below 75.

Link to save:

https://www.dropbox.com/s/ngcj2uwfjt60g7g/RSB-42.GC3Crusade?dl=0

Edit: planet name is Straim V, was originally conquered by me, I didn't think of looking at the stored goods right then.

Resources are quite difficult to come by in my current game, so no luck to spend my stored goods there.

But no matter how much social production one can get, there should be a sensible possibility to use it. To counter such amounts of social production per turn as you have, projects could have an exponential increase in costs like in my example:

75 prodution -> 25 BC

750 production -> 125 BC

7500 production -> 313 BC

So you could buy time with large amounts of social production, but that would be very expensive.

You need a saved game for something which is a feature of the game and is working exactly as the OP says even before pre-retribution, systematically and consistently? Any one playing GC3 knows that social production accumulate in-definitively when there is nothing to do. The only change in retribution is that you now have an entry for that in the middle panel, whereas before you could see the accumulated production as a tooltip in the (empty) build panel.

Now if you don't play the game, I can understand you missed that.