There have been several incidents in the past.
If you've heard of “Project Cinta”, the dakwah movement of the 1980s, or the disparate treatment of the Orang Asli, then you will know about the underhand tactics of these forced conversions.
Project Cinta is basically the "love-them-and-leave-them" project. It allegedly occurs mainly in Sabah and Sarawak.
Coerced conversions were mostly involuntary, but some opportunist non-Malays did weigh their options...