Sorry for the late responce, just going over 0 responce items. In 16.5 there are 2 basic steps.
1.) Setup the embedded layer/s under the Setup pulldown under "Embedded Layer Setup..." Probably use Body Up with Direct Attach.
2.) Make sure all the embedded components have the Embedded Placement property and a value of Required.
You will need to be in pre-select placement mode to see the command to move the part to the inner layer.
By the way, this also works well for rigidflex designs where parts are not on the top layer.