I fully understand your predicament because I also faced similar situation when I was working in Railway. However, there is no solution or short-cut, because, it would not be possible to know which examination (and interview) you would finally qualify. NoC will not be granted if you apply at the last stage.
The solution is to go on applying through proper channel and sending an advance copy in case of every examination to the department where you are applying. You have to keep record in respect of every application sent to your Departmental Head. This is important. Even if your present office doesn't forward your application, if you are selected, you will be able to submit proof that you applied through proper channel. At the same time, there is a less-discussed provision which states that if the department doesn't specifically reject your application through proper channel within a reasonable period of time (usually 15 days), you application will be deemed to be sent through proper channel (even if not actually sent by the present office).
Beware! I question everything and everybody.