If you are going to stay at one weight I would recommend rep cycling. Find a weight that you can safely do for 20 reps, 10 reps, 5 reps and 3 reps. Start with the 20 rep weight do a full body workout 3 times a week for 4 weeks starting at 70% of that weight and moving to 100%. Then do the same with the 10, the 5 and the 3. You can trick your body into thinking you are progressing that way.http://www.hypertrophy-specific.com/hst_index.html
These guys were the starting point for this kind of thing.