Shoot with a very wide angle lens and enlarge extremely.
Overexpose it. (Sounds like your plan already with long exposure and large aperture).
The Dektol may do the trick.
PE told me the rule of thumb, develop for as many minutes as you dilute it. (1:5 for 5 minutes, 1:9 for 9 minutes etc.)
You will end up with a very dense negative. That should be plenty grainy by the time you print it.
p.s. Wait for more replies from people who have done it. (I've developed a few negs in Dektol but didn't try to print it yet.)