Making a grounded object capacitive
Your basic problem is that you have a relatively small resistance accross your capacitor.  This resstance is dominating when you try to measure the capacitance.

You are trying to measure something that doesn't make much sense.  You have to decide what exactly you are really trying to measure.  If you want to measure capacitance between two conductors, then the resistance between them should be quite high.  Otherwise, the capacitance will be hard to measure and it is unlikely a usefull metric even if you could measure it.