We have never had the kind of problem you are describing. We have tongues and interpretation fairly often, but usually there is a time in the service when the Lord opens the door for it. Perhaps you need to teach the people about how to wait for the right time. Paul explained that 'the spirits of the prophets are subject to the prophets' (1 Corinthians 14:32). This means that the one speaking out has control over when he speaks. We have taught our people that even though they may feel an utterance coming on, they should wait until the time is right. We find that the right time is usually obvious.