One possibility.
Thomas Corkill's age was 56 on March 30 1851, the date of the 1851 census, and 66 on April 7 1861, the date of the 1851 census.
If his information is correct, he was born between March 31 1794 and April 6 1795.
Only two christenings in the IGI fit that time frame.
1. Thomas Corkel christened December 14 1794 in German, the son of Matthew Corkel and Margaret Skealee.
2. Thomas Corkil christened April 12 1795 (assuming he was born a week before he was christened), in Braddan, son of Thos Park and Elinor Corkil.

The IOM 1851 census only has one 56 year-old Thomas, a married labourer born in German. Unfortunately he is 68 in 1861.

However that makes Elinor's son a possibility for Cornwall.

Elinor was the daughter of William Corkil and Jane Callow and christened on June 29 1777 in Marown.

I did not find a marriage on the IGI for William and Jane. Perhaps they married on the mainland.
Also note that John Blake Corkhill's (b 1773)parents were William Corkhill and Jane (no maiden name).