Once. I did my Fat Sam beer (posted in the database I believe) and didn't have enough malt, so subbed Munich malt, and then subbed hallertauer hops for aroma/flavor. It tasted like a German ale- kinda weird but lots of people loved it.
I love northern brewer hops, but I'd probably do something totally opposite of what you're suggesting. I'd use perle and hallertauer for bittering (or whatever I had) and use northern brewer for flavor/aroma. Then it'd be like an Anchor Steam type beer.