Another idea.
What if we use some special name for first block argument to mark it as implicit receiver?
Would it make quite obvious from first look what’s going on here? 
App.routes do |it, two, three|
get :foo, two, third
end
Or maybe…
App.routes do |&., two, three|
get :foo, two, three
end
Or…
App.routes do |&, two, three|
get :foo, two, three
end
Also works with
App.routes { |&, two, three| get :foo, two, three }
Calling multiple methods on implicit receiver is nice (the &. doesn’t allow this):
[1, 2, 3].map {|&| "#{to_s} : "{to_s(16)}" }
Expands to:
[1, 2, 3].map {|n| "#{n.to_s} : "{n.to_s(16)}" }