You absolutely can. Even if you are over your allowance (or not out long enough to even have an allowance). I came through the Nexus lane last month with double my alcohol allowance. I declared it all and the officer asked if I knew what my allowance was and that I had exceeded it. I said yes, that was why I declared all that I was bringing back and was prepared to pay duty on the excess. He said ok and let me through with no duty. He was testing to see if I actually knew what my allowance was or not. He said if I hadn't known and thought I was fine it would have been a serious problem as Nexus holders are expected to know the rules. But because I knew the limit, knew I was over and because I declared honestly, he just let me go through. There is no rule that says you can only use Nexus if you are within your allowances - you just have to declare honestly and be prepared to pay duties.