Rewrite rule with deleting a pattern or backward reference in the path with AWS ELB

Using AWS ELB, I want the folowing rewrite rule :

https://example.com/dl/toto.jpg should transform to https://dl.example.com/toto.jpg

I tried two ways to do this :

• matching path /dl/* and return a path deleting /dl/ somethink like #{path/dl//}.
• use a backward reference to the match with /dl/\(*\) and replacing with path \1

2 method return invalid path message :(

Is it possible to do this with AWS ELB ? And if yes, how can I do that ?