Two AppleIDs on One Mac

I am really wondering. My wife and I just spend a fair amount of money to get a 27in iMac and had had 2 Apple IDs in the past. So we don't interfere with each other's iTunes account.

This worked fine under Windows having 2 different Apple IDs under 2 profiles.

Now we can only have one ID per iMac? Any work around, it is silly!

If not we have to wait turns of 90 days to see our past purchases. Or create a whole new Apple ID (shared one) and transfer all purchases? This is just silly that we cannot have one Mac and two IDs. What if my kids want their own account?

I understand this is difficult as they want to avoid transfer of downloads but in the good old days, if I bought a CD, my wife was listening to it too. Sharing.

Any advice?