Should be very easy, but I lack node manipulation knowledge and couldn't find the magic code words.
My only familiarity with Dynamic Guides has been the annoyance of accidentally turning them on and not knowing what they were so that I could turn them off. That said, I did just mess around with them a bit. I was still having the issue of a new node not being at the perfect center of a shape, when created with the freehanded double click of the node tool, eyeballing the location I would guess to be the center. Unless I am using the guide wrong. Incidentally, I also checked out the Alignment Guides and that actually worked nicely. No matter where I create the new node, once I drag it up and near the center, it snaps into that 0.5 location and runs along the guide. However, I think I prefer the macro (or built-in function) to toggling guides on and off for this one effect.
(Side note. I can't figure out why, but the shortcut for DGs Alt+Shift+D does not toggle the tool, rather it opens a new instance of DRAW every time I press the combo... weird. It is the assigned shortcut for the guides. I can't even try to assign it to another tool in the preferences because when I type it in to find the conflict, it just opens another instance of DRAW again.)
If you select the Lead node and tap the + key on the number pad it will place a node exactly between the Lead node and the Following node.