Here's a FAQ that provides some of the answers.
http://msdn.microsoft.com/smartclient/understanding/netcf/FAQ/default.aspx#11.18I think you can't just copy files to the device directly via a copy command. You need to set up some sort of mapping first before that will work and apparently some of the power tools provide this connectivity mapping interface.
I suspect there's someway to reference the ActiveSync device folders, through some special OS sytnax or API call, but I don't know what it is.
Let us know what you find. I need to do this too shortly...