Basically, brew a barley wine. There are quite a few strains from Wyeast that can tolerate high ABVs (up to 12%) such as 1728, 1084, 1762. Even 1065 can tolerate up to 11%.
If you do a 2/1 dilution with water to beer of a 12% barley wine, you're looking at a nice, sessionable, 4% ABV.
If you...