Thanks Georgios that looks like what I was after.  I assume the back-ticks will be treated as null values.

I should mention that I am using Maple2018.1 for this and I noticed that others have been having similiar trouble with this version of Maple, see Fabio92's post: https://www.mapleprimes.com/questions/225220-Maple-20181-Gets-Stuck-When-Trying

They are constants for a particular solution, but essentially parameters that I want to remain in the general solution.