@Alnus Rubra, thanks for this Scotch introduction.
I can't give electrical advice, because it's beyond my understanding. But as a good guru I could provide something for mind and soul
@kit brady: Depending where you live and how much this desired function is driving you, contact the PTC being resident of the US or a European (maybe UK) resident, then call PRS Europe with their Technical Centre (head: Nick Fraser) to draw this mod on your 513.
BUT: It will take the magic of versality of this guitar model. And you can switch both switches in extremis in the same time going from neck HB to bridge SC.
And taking another metapher: It's like having a Fireblade with open 217 HP and you limit the engine to 34 HP, because you like to drive slow.
If it's a crucial need I recommend you better to sell the 513 and buy a 509.
It has mini switches for the neck and bridge side of the moon and one 5 way blade switch to go through the positions. Throw the mini switch to SC sound at bridge position, you have what you want. But the 509 has a lack of one whole voicing level compared to the 513. The 513 has - owls to Athens - SC, Clear HB (likewise P90 or Mini HB sound), Heavy HB, whilst the 509 has SC and HB (but more vintage voiced with less output, therefore depending on your gain capability of the amp, a booster is needed to realize the same output like the 513.