Normally, you'd use an eVar (with Most Recent allocation and Purchase expiration) to track that link, e.g. track the link's name to the eVar. Then, run a report freeform table with that eVar as your dimension and "Transactions" / "Orders" as your metric.
The downside is that you could be tracking more than one link with that eVar, but you really only want to report on just one particular link. In that case, you could have one eVar that just tracks that one particular link (which is kinda ridiculous, but hey, it's pretty much guaranteed to work for your specific use case).
On the other hand, I don't know if one specific link is all that special to your overall purchase conversions. You might find that having a Linear allocation for that eVar could yield some pretty interesting results of your users' path to purchase.