I think the Cost Plus World Market next door to the Century theater in Evanston will let you do a mixed 6 pack. I dont think that Evanston First Liquors lets you do it, but they do offer 2-packs (taped together singles) of several of the big bottles of German beers, mostly Weiss. Stupid Evanston liquor laws!
Not sure how long you have been away from the area, but a couple more beer-thoughts. You cant break up the 4-packs, but I highly recommend you try some Half Acre beers, they are brewed just a few miles away in Lincoln Square and are available in E-Town. Their Daisy Cutter pale ale is amazing. Also, I recommend stopping by Prairie Moon restaurant in Evanston for a really great beer selection, tons of rare bottles and about 16 or so beers on tap and hand pull. Food aint bad either.
Lastly, you may not be aware that a new spirits distillery opened in Evanston (of all places!). It is called FEW Spirits and is in an old garage behind and just north of the big modern apt building near the intersection of Main-Chicago on the west side of the street.