Query about slang "scootch"-- Why -ch?

[Cohen, Gerald Leonard]

  The wife of a colleague has asked me about slang "scootch" (move a small amount), a term I had never heard before. The term clearly derives from "scoot," but how did -ch get added to it?

     The Online slang Dictionary (http://www.ocf.berkeley.edu/~wrader/slang/s.html)
says only:
 scootch   v   1. move a small amount; SCOOT. ("Scootch your seat over here."   "We'll just scootch them together.")  Submitted by Kay Turner, Bella Vista, AR, USA, 28-11-2002.

   Meanwhile, the woman who asked me about "scootch" indicates that her family has been familiar with the term for some time:

"[...]It sounds like a blend to me.  But blending "scoot" with what?  I can't think of a "ch" word that means to move over a little without picking the object or oneself up off the surface.  I also have the impression that it's used - at least in my family - to mean to move over a smaller distance than a "scoot" would require.  Like a "smidgen."

Any ideas?  She's 90 [i.e. her mother-in-law] - just had a big celebration for her in KC over the weekend, and sure enough, the word came up - often - and she mentioned she surely would like to know how and when we started putting the "ch" on "scoot" - and why.  She's mentioned this in previous years, but with family from all over the country and Canada there - all using the term - it became a real curiosity for us all.  Would please an old lady who is an appreciator of words to have an answer! [...]"

 Would anyone in ads-l have any suggestions on this?

Gerald Cohen