I think this is a widespread misunderstanding about GPL, and I am afraid it is the reason why businesses typically have a GPL-aversion.
Now, my current employer... Email your manager: "I wrote this entirely in-house and would like to open-source it." Manager: "OK, let's talk to Legal" Legal: "OK, get at least one other person to verify that it doesn't contain any trade secrets and sign this." Upload to github. Done.
And submitting patches upstream - just a matter of code-review and sending it out. Now that's OSS-friendly.