Conditionally use PLINQ with minimal code duplication

Question

I have some LINQ code that under some conditions, which I can test for, benefits from parallelization. I would like to use PLINQ when such conditions apply, but also avoid to have all the processing code written twice in different places.

What I tried to do is something like this:

var list = ...
bool doParallel = ...
var listEnumerable = doParallel ? list.AsParallel() : list.AsEnumerable();

var result = listEnumerable
      .Select(...);

This doesn't work though. listEnumerable is considered IEnumerable and the Select called is always Enumerable.Select, the single-thread one.

Edit: the answers in C# How to use AsParallel conditionally or attach dynamically at runtime do not answer my question because I am asking how to avoid exactly the kind of duplication suggested therein.