You basically have to wait until you are starting to feel withdrawals again. If you are still comfortable and feeling good.. there's a good chance that there is still too much suboxone in your system.
Being on 8mg's for a week, you have a build up of sub in your system, with the doses stacking on top of each other and the long half-life. Everyones metabolism is different so some people can get high quicker than others... some people have to wait days before an opiate will work.
8mg's is a high dose, and suboxone has an average 36 hour half life.. so even if you're on the lower side and it's 24 hours for you, that means that only factoring in one dose of 8mg's, 24 hours later you'll still have 4mgs in your system, which is definitely a blocking dose. Now, factor in the build up in your system from taking it everyday and chances are to get enough of your high to make it worth while, you'll have to wait 2 or 3 days at least.