Change file kind / kMDItemContentType
Explicitly set it within the file itself. 

Right click (or option + click) the file > Open With > Other... > TextEdit. 

Alternatively, you can use a text editor such as nano or vi within Terminal. 

Set the attribute below the shebang line

#! /bin/bash

kMDItemContentType = "public.unix-executable" 

#Rest of your shell script


I just tested this on a script in my bin:

njboot$ mdls /Users/njboot/bin/jpgrm 
kMDItemContentCreationDate     = 2014-06-10 06:06:53 +0000
kMDItemContentModificationDate = 2014-06-11 19:58:23 +0000
kMDItemContentType             = "public.unix-executable"
kMDItemContentTypeTree         = (
    "public.unix-executable",
    "public.data",
    "public.item",
    "public.executable"
)