The British did not use any technology to to make Indian farmers cultivate Opium. Instead, they forced Indian cultivators to grow opium in the following ways.
1. The British offered cash advances to poor farmers to grow opium. After taking the advance, the farmer could not grow any other crop except opium and was required to sell the opium at a low price to the British.
2. The farmers were prevented by force from selling the opium to other traders. This was even done in princely states outside British control.