Parametrically trim at intersections of straight line geometry

Hi,

is there a way to trim 2 geometry lines parametrically in ORD which cross each other?

I'm creating a junction using 'chamfer between points' for the channel which has worked well and trimmed up but I also need to put the back of kerb line offsets in to create a surface for the footway (I can't just apply a linear template because as you can see from the white lines it's a square shape). I've offset all the channel lines individually but as you might expect they overlap. I don't ideally want to use another 'chamfer between points' for the back of kerb behind the chamfer channel (although it would work) because the offset needs to be perpendicular to that channel so I'd have to workout and input an unusual offset from the 2 side back of kerb lines.

I've fudged it with a tiny chamfer for the moment but is there a better way to do it?

Thanks,

Ken