The right thing to do is to have the reduction code log matching ids on the augmenting and reducing lots, so that a single pass over the entries can then gather all the trades (combinations of augmenting and reducing lots) from any subset of transactions. I've been getting by on custom scripts so far, and it's something I *really* want, and had a go at it one evening a few months ago (
https://github.com/beancount/beancount/tree/trade_quick_experiment), but as always, the devil rears its ugly head when we get to the details and this requires more than just a bit of hacking.
v3 will *for sure* have this built in and it'll be clean. For now, you'll have to write a script to pull together your trade data.