It won't give you accurate readings. You want to know the tempurature of the exhaust gas as it's exiting the head, not after it's been through the turbo. The purpose of the gauge is to get an idea of how rich or lean your running inside the combustion chamber, not just how hot the exhuast gas is after it comes out of an already hot turbo. Take a weekend, pull the manifold off, tap and if possible, weld on a bung to the manifold, make sure it's clean and no metal shavings are going to end up in the turbo and reinstall everything.