Add a document as an attachment without uploading a local copy

Currently, I can add an attachment as a link or upload it as an attachment. Our pre-sales place a document in our CRM environment. This then ends up in an Shareepoint library. Our internal sales must add this as an attachment to a quote in SalesBuildr. We want to avoid them having to place a copy locally before they can add it. So, I'm looking for an additional way to add an attachment, possibly via drag & drop from this SharePoint library?