While Nina does not have custom pre-order functionality yet, you can create a preorder by using the Release Edit tools on your release.
1. Upload the song(s) you want live now along with the album art
2. Set the price for the album (note: this cannot be changed)
3. Publish release
4. When the full album/ep is ready to go live, go to the release page and edit the release by adding new songs and updating the description