Partial solution (adding reroutes to all unused inputs and replacing them) :
If you prefer to read or didn't understand this rushed video :
So you have a bunch of nodes and you want to add reroutes to their inputs
- add any node (doesn't matter which one since you'll delete it later)
- move it on the left of your bunch of nodes
- select your bunch of nodes and the new lonely one which you set as the active one
- press K (with Node Wrangler enabled) to connect the lonely node to the bunch of nodes.
- select and group the entire node tree except for the new lonely node which stays outside
- in the group, Shift + left-click drag on the group input links to add reroutes on them
- Tab to get out of the group
- Alt+G to ungroup it
- delete the lonely node you added previously
- reorder your reroutes properly if some are not in the right place
- Shift+= to arrange them perfectly
Voilà. Now you can replace those reroutes by any node with Shift+S. And if you need them to have specific parameters, don't forget Right-click > "copy to selected" to apply your changes from the active node to all the selected ones.