quite possible but you would need to consult vestry books etc (probably in Manx Museum) - Sextons were really only made compulsory by the 1881 act as prior to this in several parishes the family was still responsible for digging grave though increasing after the 1869 Tynwald cpommittee enquiry they came to be employed - see http://www.ee.surrey.ac.uk/Contrib/manx/gazateer/gyards/cems.htm
however St Thomas's definitely has NO burial ground!