This is the lowest mass rocket to LDO i could make using existing engines and parts.
It doesnt get much lighter than that and it took me quite a bit of tweaking and changing small things to get it below 1t.

Also: no xml editing or tinker panel was used!

Ascend profile:
Turn to 45° almost imideatly after liftoff and keep it untill first stage burnout. Then try getting your apoapsis out of the athmosphere with the second stage.
Deploy the fairing as soon as you get out of the atmosphere (mach number changes to zero) and deploy the last stage.
Now keep the time to apoapsis as close to zero as possible without making it zero for the rest of the ascend and you should get to orbit with 100 or 200m/s of dv left.