>>1408850firstly make sure that you thoroughly clean and grease everything so that the bolt doesn't need much torque to hold
Also if the tube has been bent to fit a narrower post than intended, bend it back out and find the correct size post
Don't worry about breaking the clamp when using the correct size post and it's all greased. If it's rusted out, it's rusted out. You'd have needed to repair it anyway
slightly left field idea, but instead of repairing it, you can actually buy (or make, there are guides for making one online) a quill seatpost. You would want quite a lot of insertion though as the bottom of the slot would count as the top of the tube.
