I am sure you can give it a go. I have done a upgrade difference of 3 versions once and it was fine. But I would do stepped upgrades myself and I wouldn't expect, (or want the Sitefinity team to put time into), to support such a upgrade scenario.
Me, I upgrade all the time. I upgrade my customers for free because upgrading from version a to b is always fully supported and generally issueless. (Plus I get heaps of bug fixes and improvements and that only makes the customers happy)
I am not of the "if its not broke don't fix it." I have vb6 projects that ain't broke but who the smurf wants to be dealing with those now?
I like it to upgrading VS 2003 projects to 2010, (Of which I have done 30 in the last 4 months) Too much has changed and I upgrade version to version and have no problems. (If I try the big jump I do)
(And I think this applies to most apps and there upgrades. (We'll at least Microsoft based ones.))
Upgrading a SF project would be the same. You upgrade locally a few versions at a time and do one prod upgrade at the end.
I totally understand that in your environment, this may not be easy. But, if that is the case, I would encourage you to look at why that is and change things so going forward you can.
Not the answer you were looking for I know, but perhaps a change of thinking might be better here.