That would work. One Dioptre is a common size for supplementary close up lenses (it looks like that is what you are using already) the most common being the Canon +1 lens with a 58mm thread.
Originally Posted by m1tch
They seem to be available in 1, 2 and 4 Dioptres but not 3.
The adding of Dioptres method technically only works for lenses very close together but I think all of yours will be close enough for it to be a good approximation.
Something I learned here was that if you put a positive and negative lens together, you can create a degree of zoom by moving them apart.