Ok, maybe it was a stupid idea to use my main char as example. The idea is to set up a crime scene with an mule to spark an role play.
If you want to RP a corpse as a way of launching an RP story, then go for it. Since a 'corpse' seems to indicate 'true death' as I understand it defined by settings, then I would suggest using an alt that will be deleted after the disposal of the corpse. If you take the pose (lying down) out of the possible tools available to you at this time, you still have other options left.
1. Character description:
Get creative with the physical description of the corpse. Include visible clues that are apparent to anyone standing over the body and looking at it. Include things like scars, torn clothing, unusual skin coloration, etc. Make your target audience look for these hints and clues.

2. Actions:
The /my command is your best tool for providing interactive feedback and deeper clues if someone is attentive enough to know what to look closer at. A corpse can't speak, but can still be a character.
Examples:
Player: /me examines the back of the corpse's head.
Corpse: /my head has a wound that appears to have been caused by a blunt object.
Player: /me examines the body's pockets.
Corpse: /my pockets are empty.
If you want even more impact, have the future corpse be seen while still alive. Make him a real character and play him for a few weeks before his unfortunate demise. Give him a 'normal' description and then change the description as appropriate as soon as he becomes a corpse. If people meet him while he is alive, there is a more personal connection to him. The more 'different' or 'quirky' the character, the more likely he will be remembered. The point is to 'make him known'. Depending on the circumstances surrounding his demise, clues can dropped while he is alive as well ... clues to something that is going to happen to him. This part isn't necessary and may not even work with what you have in mind. I'm speaking in general terms only since I don't know the details of your idea.
Under the moon has pulled this sort of thing off beautifully in the past and may be able to offer additional suggestions that I have overlooked.
As far as the posing of the corpse, that is a relatively minor issue and can still be handled with some creativity either in the description or with /my. Just have the corpse sitting and propped against a wall.

Good luck.