I use the multi city booking tool on DL. For example, if you want to spend a night in Atlanta in route to MSP, you would book EU-ATL for one segment and the following segment would be ATL-MSP for the next day. Your final segment (assuming no stopovers on the way home) would be MSP-EU and you will be presented with connection options.

Note: I have only done this with domestic trips, so not sure if there are rules that prevent this on international itineraries. Someone else will have to chime in.