Looking up a substring

I have a situation where I need to lookup against just a portion of a field (i.e. the equivalent of LIKE in SQL). How can I make this happen in data services as it seems I cannot manipulate the column in the lookup table as part of lookup_ext.

As an example.

I have a source email field with jsmith@abc.com

My lookup table has jsmith1@abc.com

I want to lookup and find that jsmith1 record as a match.