Pretty sure your LSDAS account lasts for five years, so your recs should stay there for 5 years.
Alternatively, depending on how big your school is, your pre-law office could create a dossier for you. My pre-law office offers to do this for people who know they are taking time off. Professors send the recs to them (with the LOR forms, of course) and the pre-law office sends them in to LSAC when you are ready to apply.
There are also other dossier services like Interfax (might be getting the name wrong)