mathspec com símbolo grego itálico minúsculo std

Question

Eu gostaria de obter a greek symbolsfonte symbol std italic. Meu MWE é:

\documentclass{article}
\usepackage{mathspec}
\setmainfont[Mapping=tex-text]{Times LT Std}
\setmathsfont{Symbol Std-Italic}
\setmathsfont(Digits){Times LT Std}
\setmathsfont(Latin)[Numbers={Lining,Proportional}]{Times LT Std}
\setmathsfont(Greek)[Lowercase=Regular]{Symbol Std}

\begin{document}
This is some sample text. $\alpha$ Sample lowercase Italic $\beta$.
\end{document}

Ou posso usar unicode-matho pacote, como?