A better strategy would be to recruit someone who already has access to the information you want. Consider the difficulty in "placing a loyal agent":
1. Getting them into the country setting up a life for them,
2. Getting them through citizenship (might take five-twenty years, might never happen),
3. Getting them hired at the CIA and hoping they get sufficient clearance,
4. Getting them moved in to a role with access to the information you want.
2,3,4 all require a number of things going right, nothing going wrong and each would take many years. Success would require a large number of attempts and the successful attempts might take over a decade before you get useful intelligence. I'm not sure anything like what you suggest has ever happened, the closest I can think of is the technique of placing agents in a foreign country and having them associate with targets of interest or report back intelligence[0].