Edd,
Read your mail and was a little surprised.
The Eclipse Cocker is piece of kit, it's no Tipman, but what can you do
Why would you want to push the marker back or touch the grip frame for that matter.
If you do the balance of the entire marker will be destroyed, unless you have arms like absolute tree trunks you'll be shooting shots all over the place.
Plus, I had a friend who did something similar, moving things forward restrict your shooting angles and restrict you when lane shooting.
I would say leave it how it is, or by a Tipman (meant Angel)
Hope this gives you something to think about.
Pete