How frustrating is it to change GOPATH? In each GOPATH, create a file called "source" or something, and put the following in it:

  export GOPATH=/home/ubercow/project2/

Or even:

  export GOPATH=`pwd`

When it's time to work on your project just say

  . source

This seems like an INCREDIBLY minor step to take. It's certainly no worse than using pyenv.