How can I mock an array's sort expect a lambda expression?

This is a trivial example of my problem:

# initializing the data
l = lambda { |a,b| a <=> b }
array = [ 1, 2, 3, 4, 5 ]
sorted_array = [ 2, 3, 8, 9, 1]

# I expect that sort will be called using the lambda as a parameter
array.expects(:sort).with( l ).returns( sorted_array )

# perform the sort using the lambda expression
temp = array.sort{|a,b| l.call(a,b) }

Now, at first I expected that this would work; however, I got the following error:

- expected exactly once, not yet invoked: [ 1, 2, 3, 4, 5 ].sort(#<Proc:0xb665eb48>)

Is there a way to do what I am looking for?

Cheers, Joseph