bash: setting environment variables from a script and leave a shell prompt

bash: setting environment variables from a script and leave a shell prompt

I'm looking for a way to create some kind of a 'setup' script that would
set environment variables and at the end leave the user with a bash
command prompt.
for example:
#!/bin/bash
export PATH=...
export LD_LIBRARY_PATH=...
export PS1=...
...
<give a shell prompt with the above environment variables set>
I don't want to source a file with the environment variable settings since
I'd like the user to be able to 'exit' back to the shell where this
'setup' was launched.
How can this be done?