[ruby-core:33721] Suppressing "assigned but unused variable"

I have stopped assigning many unused variables thanks to this new warning.

I have a spot where the warning is false, though:

$ cat test.rb 
def b
  a = :some_value
  binding
end

eval 'puts a', b
$ ruby19 -vw test.rb 
ruby 1.9.3dev (2010-12-15 trunk 30218) [x86_64-darwin10.5.0]
test.rb:2: warning: assigned but unused variable - a
some_value

In this case, a is captured by the binding for later use, but ruby warns anyway.

I can work around this warning by double-assigning a:

def b
  a = a = :some_value
  binding
end

But that looks ugly.

Is there a better way?