You can change the DefaultInlineFormatType for "Text" cells to DefaultInputInlineFormatType (i.e., "StandardForm"), and change the style "InlineCell" to inherit options from "Input":
SetOptions[
EvaluationNotebook[],
StyleDefinitions -> Notebook[
{
Cell[StyleData[StyleDefinitions -> "Default.nb"]],
Cell[StyleData["Text"], DefaultInlineFormatType -> System`DefaultInputInlineFormatType],
Cell[StyleData["InlineCell", StyleDefinitions->StyleData["Input"]]]
}
]
]
Here is screen capture from a notebook, showing a text cell with an inline cell, followed by a normal "Input" cell, so that you can compare them:

InputForm. Is there a way to automate this process? – Naitree Apr 18 '14 at 06:22