The only thing that could help would be to have a permanent prime remover like on the BfB3000.
On the Rapman, the prime remover only consist in a hole in the front-right corner of the print bed, also known as the rest position (or heating position).
For the very first layer being printed it's usually efficient and cuts the filament correctly. But the more the bed goes down and the less efficient it becomes.

In the case we're discussing about - use of the support feature with different temp for the support - the prime remover won't be efficient in removing the filament string that comes out of the extruder while it rests (change its temp). Because the hole gets too low.
What we need is a prime remover that would permanently stay in place.

Having a look at the Rapman it's evident that the prime remover will have to be fixed somewhere near the rest position (front-right). But there isn't many possibilities where to fix it to the Rapman's structure.
The best idea, again, is making use of the extra setting jig that I have left.
By putting this setting jig along the right Y axis it will offer an easy way for fixing a prime remover.

Now let's go in SketchUp for the design part... And that's how it's going to be :

Prime remover

And that's the prime remover printed :

(photo will be added soon...)

And here it is in place and fixed to the setting jig : I will tell you if it's efficient the next time I will have to do a print that needs some support...

(photo will be added soon...)