Thank you so much for your time as well! I appologise for not responding to your email earlier - I have that awful flu that is going around.

I would love to be on stand-by and take on any work that you may need to have done. Please let me know if you need anything else, or if any of your other candidates don't pan out, as I would be interested in that full time in-house position.
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I would start the second paragraph with something like "While I appreciate your interest in me as a Stand-by, I also hope you are also considering me as one of the candidates for the full-time position.

If you spoke to Mr. last boss, please take his response with a grain of salt, as he is untrustworthy and has been bad-mouthing me for his own personal reason, which had nothing to do with the work I did for him, or my job there. I would happy to supply other, more trustworthy references, as I worry he may prejudice any furture employers."