Working as a freelancer while in the employ of a company in India

My friend works for an Indian firm. In his offer letter is the standard ‘you cannot accept work elsewhere clause’. He’d like to be able to work part-time at a start up.

Question:

  1. Can anyone tell me how he can do that in good conscience?
  2. I see famous folks on social media promoting their books, their courses, getting sponsored on Youtube videos etc. while in the employ of a company (contemporary example - Krish Ashok - Masala Labs book - TCS employee) How do they do it?

I am relating this query to the IFF’s theme in the following way - an employer’s offer letter as a piece of rule/legislation. If anyone knows of any other forums where such a question might be better suited, I’d be grateful to know about it and pull this post down.