Mak,
tell the customer that you can not do it for ethical reasons. You may lose a customer, but if it spreads that you have refused for that reason you should gain many other customers.

Raghu,
An attempt is made to copy code. Whatever arguments one may have for it - "the user wanted it so " is one such. But tell me why would one want to do that ? Can there be any reason OTHER than to save the cost of buying the whole equipment based on the MCU ? If so I ( and the forum )will be very interested to know THAT other reason.
While I wholehartedly support the "do not help with copying code" attitude - especially when it "smells" like the one here (mask programmed chip) I must - in reply to your question - tell about the one case where I copied code.
A companys building burned and the company - stupidly - did not have any offsite backup. They bought one of their own units back from a customer and asked me to reverse engineer it. I made some attempts with disassembly - some of you have seen my comments on that subject - and finally re-engineered the unit instead of reverse engineering it. In the meantime some units were built with direct copied code and while they "worked" I did not find the reason for a "slight glitch". Copying a chip and inserting it in a copied board is a true nightmare - how do you debug something you do not know what is.

Erik