Is it possible to define what size (i.e. MEDIUMBLOB) SQLObject creates for a BLOBCol (specifically for MySQL)?

example (from TurboGears):

class Book(SQLObject):
    isbn = StringCol(length=13, alternateID=True)
    title = StringCol(length=100)
    description = StringCol()
    authors = RelatedJoin('Author')
    binvar = BLOBCol()

Will create a TINYBLOB column in the actual database, but I need a MEDIUMBLOB.

If I can't specify the size directly with SQLObject, is there any problem with just modifying it with MySQL?