Extending Alignment in C/C++ expressions (align.el)

[Nordlöw <per.nordlow@gmail.com>]

How can I extend the Emacs package align.el to make M-x align-entire
additionally align the if sub-expressions and opening curly-braces as
follows?:

if (x) { xi = -1; }
else (yyy) { yyyi = +1; }

should be aligned into

if   (x)   { xi   = -1; }
else (yyy) { yyyi = +1; }

(the example needs to be displayed in fixed-width font to be
understandable)

Thanks,
Nordlöw