Can I merge phone and email iMessages?

I have a contact that has both their phone number and iCloud address linked to iMessage. On my phone (iPhone 6, iOS 8.3) I have 2 separate conversations from them - one where the message is sent from their phone number, the other their email address. Is there any way to merge these into a single, unified conversation? Both their phone number and email address are stored in the same contact card. Thanks!