Rear end sag - the car's not mine

My '93 Regal is sittin' pretty low in the a** end even with the trunk empty. What are the options here? Can the glass spring be recurved? Do I have to replace it? What about helper springs? I've done some searching and haven't found much. I often load up dj gear and sometimes haul my atv trailer. Struts were replace by the po shortly before I bought the car so they should be good to go for awhile yet. Thanks!