Deploy lambda function on already created resources without cloudformation

I am faced with a challenge where I do not have access to create resources. Usually serverless creates resources via Cloudformation by uploading a CF template and asking Cloudformation to create the stack.
In this case, there will be no stack as such but the resources required will be already created for me.
I want to deploy the lambda function and all code on the existing resources like API-gateway, S3 bucket, Lambda role, Lambda function which are already created manually.

Is it possible to bypass cloudformation ? Or is Cloudformation mandatory ?