\documentclass{article}




\def\FontWithCMap#1#2#3{%
   \font#1=#2\relax
   \immediate\pdfobj stream file {#3}%
   \pdffontattr#1{/ToUnicode \the\pdflastobj\space 0 R}%
}
\def\AddCMapToFont#1#2{%
   \immediate\pdfobj stream file {#2}%
   \pdffontattr#1{/ToUnicode \the\pdflastobj\space 0 R}%
}


\begin{document}


\FontWithCMap\test{cmr12}{ot1.cmap}
\test abcdef ghijkl mnopqr stuvwx yz fi fl ffi ffl 


\begin{math}
  a
  \AddCMapToFont{\textfont2}{oms.cmap}
  \mathcal{A} - \mathcal{B} + \mathcal{C} * \mathcal{D} \cdot 
  \mathcal{E} \bullet \mathcal{F} \spadesuit
\end{math}


\end{document}