I don't often work with .dwgs, but I'm pretty sure you can open them directly in SW (with SW open, but no files open, go to File > Open and browse to the file, making sure "All Files" is selected in the lower right corner of the Browse dialog box).
Now, you said "I also want to retain the link to the file if I need to edit it at a later time." Assuming you mean that you want later edits to the .dwg to be reflected in the SW Drawing, that's not possible.
I have to say I've never tried this before. But I just did. It does come up but as a window without viewing abilities but it is linked. I don't thing SWx was intended to work this way. My only question is once it's in Solidworks why would you want to go back to edit it in Draftsight or AutoCAD for that matter. Bring it in as a SWx sketch then pull it in to a drawing template and you're good.
Hopefully some one else will have the solution you're looking for. Good luck!!!
I've done this with MS Excel based tables that show up on the drawing and then you can click on it and edit via MS Excel.
We have electrical drafters that make the schematics specifically using 2D CAD tools like AutoCAD and Draftsight that we use in our electro-mechanical designs that I want to embed into the drawing file. When they make changes (or myself for quick edits), I would like the drawing view to update. Hence the reason to maintain edits in the native file format.