What kind of LES would be optimal for this shuttle, in your opinion? Would an Eridanus-style LES work, or would it be too dangerous during max Q, or incur too much of a weight penalty in general?
MaxQ would be a problem, but I also see some trouble there with the direction in which it fires - it does not quickly separate from the rest of the launcher, but launches straight up in the first seconds. So, even normal aerodynamic forces would rather pull it towards the stage first (similar problem as dropping bombs from a fast aircraft, which is solved by huge pyrotechnic forces in the bomb pylon), instead of away. And gusts and high attitude rates would also be a problem.
Then, it is of course a bit bad to mount a LES at the place where any penetrations of the heat shield are rather annoying. Also you need structural reinforcements for taking the pulling loads (which are worse than compressions), which make the nose pretty heavy even after separation.
But hey, Orbiter is not reality. Colliding with the stage during abort looks bad but is not THAT bad, and structural weaknesses are not that much important.
The primary problem that you have to solve is vertical separation in the first milliseconds of abort. Pneumatic pushers could contribute to it (Like ejection seats use), but finally you need turn pitch away from the core stage fast even before you have full acceleration.
Thruster modules at the sides of the spaceplane could help there, structural reinforcements would also not be needed that much and getting vertical separation would be easier by using extra pushing thrusters, but again, they would need to be pretty heavy to allow a good abort.
It is a very tough problem, since you essentially want to do something with a spaceplane, that counters the usual requirements on a spaceplane. You have forces at places and in directions, you usually don't have. You need to fly out of a place, that you can only leave with violent force at high dynamic pressures.
Any solution has its disadvantages and will never be perfect. A smaller plane could likely abort easier than a 125 ton Space Shuttle. But it would still mean loss of performance.