You have a complicated situation, I have two possible solutions for you
If the same change-set applies to all of the associated work items (WI) then no matter which one of your work item need to be released the whole change-set will be merged. so perhaps you can associate the merge with the WI you are going to release and merge. and when it come to other WI's you can simply mark them released stating the change-set you've previously merged.
If your current change-set have multiple changes for different WI's then perhaps best solution is to rollback the change-set and check-in respectively for each WI you have. by doing this you'll have separate change-set representing each of your WI, then you can easily proceed with the merge for the desired WI.