Based on your response, the answer to your question is to create a new resource that contains that single set of information. e.g.
GET /Customer/1212/RecentPurchases
Creating composite urls that have many identifiers in a single url limits the benefits of caches and adds unnecessary complexity to the server and client. When you load a web page that has a bunch of graphics, you don’t see
GET /MyPage/image1.jpg;image2.jpg;image3.jpg
It just isn’t worth the hassle.