I would break up the alignment so I could use adding curves from end of entity (starting at S1) and go from there. Others might have better suggestions.
Start by breaking apart the PI, then you can add the pieces you need to connect the tangents. It depends on what parts of the curve-curve-spiral are constrained and which are not. I've attached a drawing with several possible combinations.
There are probably more possibilities - choose the elements that work for your situation.
Steve
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