Feature request: Allow ignoring dependencies when building with python pip

I'd like some way to set a flag, preferably per library, that disables downloading dependencies. The example I have is that I'm using the pynamodb library to interact with dynamodb, and when installing the library, it pulls in the entire botocore as a dependency. This pushes the lambda function over the size limit for editing in the console, which is quite annoying. Botocore is built into the lambda runtime, so pynamo doesn't need to install its own copy.

See https://github.com/pynamodb/PynamoDB/issues/1166