The short answer is no since all the class attributes are floats not doubles.

The solution is to create a new class that does the same as PVector but using doubles. I did this by copying the source code for PVector then search and replace float with double, I had to modify the lerp and hashcode functions by hand but the result can be seem here

To use this class then create a new tab in your processing sketch called PVectorD.java (this is case sensitive) and copy the code from the above link into this tab. Instead of using PVector use PVectorD instead it should work just fine.

Just after I posted this I had a look at the PVector source and realised that i'd asked a stupid question and I thought about whether or not it would be possible to just go through and change all the floats to doubles.

I casted all my doubles to floats after the calculations in the sketches I've been working on and I had to split what was point.x point.y point.z into 3 separate variables. I'll give it another go using your vector doubles class.