Like patching of classes, you can also patch single objects. The difference is that only that one instance can use the new method.
Example: Override a string object to provide parsing to boolean
s = 'true' t = 'false' def s.to_b self =~ /true/ ? true : false end >> s.to_b => true >> t.to_b => undefined method `to_b' for "false":String (NoMethodError)