Recycling themes

I own -amongst others- the very nice “parallaxis” theme from Weaver Kingdom (former Archetypon, which sounds nicer), but I now would like to have the parallax effect within the Retract theme from Henk Vrieselaar.
Peace of cake probably with the Parallax stack from Joe Workman, it’s only $20,-.
But something in me is against this…
Why can’t I use the effect from the parallaxis theme as a stack.
Is there anybody with a simple recycling method?
A big thank you in advance.