How can I create an issue field for target sprint?

[Elin Wiklund]

We have a large number of versions in each sprint, so using the target version field is very impractical for us; but we still want to make sure the team knows what branch a bug fix needs to be completed in. For this purpose we were hoping to use a field that would allow us to set "target sprint." Is there any way to create this using custom fields? We don't want to have to go in and update the available values for this custom field every sprint, but would like it to show just the currently open sprints.