You can use "expand pattern" or grow selection" from the context menu, but both yes, both options will always double the number of rows (i.e. insert one empty row between each two rows). If you have an existing melody, you will have to do this manually. Using the Insert key to insert empty rows inbetween might be the easiest way in that case. If you want to record a new melody, changing the "Edit Step" to the desired value will also help.
