Yes it is possible, though this would not be a recommended setup.
RDS provides a built in procedure you can call to set this up. Rather than me explaining the procedure here, I will simply link you to the documentation.
http://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/mysql_rds_set_external_master.html
What this doesn't tell you is that you must have taken a consistent DB dump from the master DB and installed it on the RDS instance. You must also have obviously recorded the binary log position information when taking that consistent dump, so you have that information to use in the procedure.