Splitting measurement variable

Measuring a variable then share to third party. Third party would have a power loop to power loop isolator (meaning they only get 4-20mA). If I set the instrument in series with the Third party, then I will brake the power loop when they are not completing the loop. What I need is a power loop replicator which it will give them, the signal and also the power.
Having call many different Industrial stores, and apparently all salesman are busy or Automation department is in vacation still for X-mas.

I will appreciate if you give a hint!!! Thanks.