Yes, you can!
When you want to release a single first and then later include it in the album/EP, you can use the "Reuse your old tracks" button when uploading tracks to the album/EP. With this handy tool, you can easily upload a single first and later integrate it into the album/EP release without losing play statistics.
Just follow these simple steps:
Release the single
When uploading the album/EP, fill in all necessary. release info.
Add the track from the previously released single by clicking on the "Reuse your old tracks" button, typing in the ISRC for the existing track you'd like to add and hit 'Search'.
Continue by adding the additional album/EP tracks via "Upload more audio files"
After this process has been completed, you can choose to either remove the original single or keep it up. It will still remain as part of the album/EP.