You won't be able to do that with MTP mode until we have a working USB stack and MTP stack for the Clip. Currently we have neither, although both are in progress.
You could try setting your player to MSC mode. I have no idea if WMP will sync AAC files to an MSC device (and if it can be made to you may need some third party expansion), but you can try. Probably your best bet is to just not use AAC if you want to use WMP.