Slow Motion

need some help
I am shooting in 60 fps, but want my final project in 30 fps I want to do some slow mo effect. 
when I do 60p project, make a part of video in 50% (30p) and export it to 60p file thanI have a slowmo part in a lower framrate (30 p) than rest of video (60p).
When I am in 30p project, add my 60p video, make a part of video in 50% , after export it to 30p file it is normal video on 30p slow on 15p.

Is there possibility to have a final video clip in 30p made of 60p file where part of video will be in slowmotion and part normal but all in 30p?
please help