Sometimes in life we might have to take calculated risk if it benefits someone. However, while providing help to someone out of way, underlying factor of trust matters lot. Your help should not boom rang on you. Otherwise, situation could tantamount to a proverb "Aa bail mujze maar".
Since the ex-employee is beseeching you, rather than handling the matter on your own, you may defer it to your MD's office. Let your MD take a decision on whether to issue backdated service-cum-employment certificate or not.
It is not a question of employment certificate alone. What if his future company asks for the salary details for the period for which employee did not work? What if the future company asks for the bank statement? In that case you will have to provide the fake the salary slips also.
Therefore, please take the call judiciously.
27th May 2017 From India, Bangalore