Q:

How to suppress undesirable kerning rules in math inline cells? 

Update:  (11/29/2012)  Looks like Mathematica 9 has the same behavior. 
The following graphic shows how Mathematica kerns italic characters in an inline math formula cell (first row) where an \[InvisibleSpace] has been inserted between consecutive characters (which could represent either multiplication of terms or multi-indices depending on context) vs. in an ordinary, non-math text cell which was switched to italics using Ctrl-I (second row). 

When the letters ijk for example appear together in a subscript as indices, the spacing between the i and the j appears too wide relative to the distance between the j and the k.  
Original Q:  Is it possible to turn off this special kerning in math formula cells?   
Updated Q:  (10/1/2012)  A reasonable but nevertheless somewhat inconvenient method to work around this issue has been suggested below.   Does anyone know the reason why the kerning rules for juxtaposing italic characters inside math formula cells are different from those for normal, non-math italic text? 

For ease of copying:
Cell[TextData[{
 "Text ",
 Cell[BoxData[
  FormBox[
   RowBox[{
   "a", "\[InvisibleSpace]", "b", "\[InvisibleSpace]", "c", 
    "\[InvisibleSpace]", "d", "\[InvisibleSpace]", "e", 
    "\[InvisibleSpace]", "f", "\[InvisibleSpace]", "g", 
    "\[InvisibleSpace]", "h", "\[InvisibleSpace]", "i", 
    "\[InvisibleSpace]", "j", "\[InvisibleSpace]", "k", 
    "\[InvisibleSpace]", "l", "\[InvisibleSpace]", "m", 
    "\[InvisibleSpace]", "n", "\[InvisibleSpace]", "o", 
    "\[InvisibleSpace]", "p", "\[InvisibleSpace]", "q", 
    "\[InvisibleSpace]", "r", "\[InvisibleSpace]", "s", 
    "\[InvisibleSpace]", "t", "\[InvisibleSpace]", "u", 
    "\[InvisibleSpace]", "v", "\[InvisibleSpace]", "w", 
    "\[InvisibleSpace]", "x", "\[InvisibleSpace]", "y", 
    "\[InvisibleSpace]", "z"}], TraditionalForm]],
  FormatType->"TraditionalForm"],
 " Text"
}], "Text"]

A:

You can redefine RowBox to automatically wrap specific characters in an AdjustmentBox which reduces the right-side spacing.   This isn't perfect but might get you on the right track. 
Unprotect[RowBox];
RowBox[chars_List  /; MemberQ[chars, "i" | "e" | "f" | "o"]] := 
  RowBox[Replace[chars , {
     "i" -> AdjustmentBox["i", BoxMargins -> {{0, -0.1}, {0, 0}}],
     "e" -> AdjustmentBox["e", BoxMargins -> {{0, -0.15}, {0, 0}}],
     "f" -> AdjustmentBox["f", BoxMargins -> {{0, -0.15}, {0, 0}}],
     "o" -> AdjustmentBox["o", BoxMargins -> {{0, -0.1}, {0, 0}}]
     }, {1}]];
Protect[RowBox];

Comparison:

This won't catch sub/superscripted characters, and it will affect all RowBoxes, not just the ones used for TraditionalForm.   I could not figure out how to do the same trick, but only for FormBox[RowBox[chars_List], TraditionalForm].   Maybe someone else can figure that part out.