Download link: https://github.com/TurielD/Civilian-to-military-spending-mod/archive/master.zip

It's a bit rough-and-ready, but it works: place the contents of the zip in to your mods folder, and when you start a new game you'll find there's now a new project called 'Shipyard Backing'. What it does is send all civilian manufacturing to the military.

(probable) Bugs:

• I don't know what will happen if you do this on a planet where there is no associated shipyard (my guess is it will crash).
• It doesn't take military production efficiency techs of race traits in to account. If your race is more efficient at civvy production than miltary, you will get more military production out of using this than you would with full military spending, that is not intentional but I haven't thought of how to limit that in an elegant way just yet.

Development link: https://github.com/TurielD/Civilian-to-military-spending-mod

I'm not very active with modding right now, so I invite anyone who feels so inclined to feel free to adapt this so that it works better, and post here!