According to the documentation (password is required, see http://docportal.sdl.com/sdltridion ), you should use the following in your DWT template:
@@RenderComponentField("fieldname", TemplateRepeatIndex)@@
But this is not so useful for Component Links, because it just displays TCMURI in your template, so you probably want it to become a dynamic link, and then you can use the following in your DWT template:
<tcdl:ComponentField name="fieldname" index="${TemplateRepeatIndex}"> <a href="#" tridion:href="@@ Field@ @" tridion:type="Component">@@ Field@ @</a> </tcdl:ComponentField>
If you need the name of the related component in this link, you can use Dreamweaver Get eXtension (DGX) .
Now you will get the value of all editable fields, and when you edit one of the fields, you will get a green plus button in the upper left corner of the field properties, from where you can add a new value (you will see the delete and move button at the top of the field properties too). 
Please note: if the field of your multi-valued value is initially empty, you need to make sure that there is a tcdl tag that allows XPM to understand that it should show field editing properties there, you can use something like this to do this:
<tcdl:ComponentField name="${Field.Name}"></tcdl:ComponentField>
For more information about inline editing, see.
EDIT:
It seems that I misunderstood the question a bit, because, as Frank observes, unfortunately, XPM does not have the ability to add multi-valued embedded fields. I was tempted to use the following construction, which allows me to edit all fields, but there are no buttons with multiple values โโ(since this is not supported):
<tcdl:ComponentField name="fieldname" index="${TemplateRepeatIndex}"> @@RenderComponentField(FieldPath+".embeddableFieldname1", TemplateRepeatIndex)@@ - @@RenderComponentField(FieldPath+".embeddableFieldname2", TemplateRepeatIndex)@@ </tcdl:ComponentField>