Biggest problem with shipping with a loose mirror is that it will probably get more damage. Opening it up yourself is going to be no loss if it wouldn't survive anyway.
I IR modded my old DSLR recently and it worked, ... for about 3 days. But it had no value as it was never going to be used as a camera again and had little if any resale worth. The experience was worth it so next camera I will be more careful but I'll have another go for sure. Just gotta find another cheapish camera ...
I'd at least be having a go at Marcs suggestion.