Lannanta - I have had a look at the May family and from what I can see the only possible link that might explain the name is Elizabeth's brother.
The Glasson name was not apparent when the birth was registered but you are probably aware that Richard was not the first May child to be endowed with the name. There was also Jane Glasson May baptised at St Mewan in 1824.
The Census is not overly helpful with creating a list of the May children with only William, Samuel, Elizabeth, James and Richard appearing in 1841 and 1851 with their parents.
The list I have arrived at is as follows although I cannot be sure about George:-
John bp. 31st December 1820 Newlyn East
Susan bp. 15th December 1822 Newlyn East (buried 6th July 1823 'of St Allen')
Jane Glasson bp. 4th January 1824 St Mewan 'of Newlyn in Pider'
William (age 15 in 1841 Census)
George bp. 3rd September 1826 Bodmin Wesleyan Circuit 'of St Columb' (born 8th August 1826
Mary bp. 11th November 1827 Newlyn East
Samuel bp. 19th August 1832 Newlyn East
Elizabeth Ann bp. 10th July 1835 Newlyn East
James bp. 9th April 1837 (Truro BC Circuit) at his father's residence Newlyn (born 13th March 1837)
Richard Glasson bp. 2nd January 1840 Wesleyan Methodist Chapel, Newlyn East (born 12th October 1839)
I am uncertain about George because of the location even though St Columb is only separated from Newlyn by one Parish. He may be the 15-year-old George May at St Enoder in 1841 but thereafter he seems to disappear.
No baptism found for William as yet but age 15 in 1841 means he could have been born any time from about 1821 through 1826. Even if he were born in 1825 there is ample room for him between Jane and George as shown in the above list.
If you can find what happened to Richard Glasson, brother to Elizabeth, it might go some way to explaining the name of Richard Glasson May.
CT