It's only fine to have a Reference letter drawn exactly as CIC requires.
All the other ways are not that safe by definition.
That's to say if there's a chance to persuade your company to give your RL as per CIC requirements you'd better go for this option. If not - make this additional RL from a project manager as close to CIC requirements as possible (letterhead, seal, signature)
There're no other alternatives here but to apply with whichever evidences of JD you can provide.
Perhaps it's possible to enclose any proofs thank your employer refused to give a letter on your JD. Something like an e-mail which you can enclose to your cover letter. And, of course, you should write a really smart cover letter to make your explanation look reasonable.
PS: Hopefully it's not the primary NOC experience we're discussing.
To be eligible for FSWP one needs to have at least 1 year of experience in any NOC listed for 2014. This is your primary NOC. Other work experience of course matters (for scoring points), but it's your primary work experience which allows you to apply at the first place.
That is why it's highly desirable to have a concrete proof work experience for primary NOC.
