From my reading you can use any valid non-ascii character for the initial one too:

  ident     [-]?{nmstart}{nmchar}*
  nmstart   [_a-z]|{nonascii}|{escape}
  nonascii  [^\0-\177]
  unicode   \\[0-9a-f]{1,6}(\r\n|[ \n\r\t\f])?
  escape    {unicode}|\\[^\n\r\f0-9a-f]
  nmchar    [_a-z0-9-]|{nonascii}|{escape}

(nmstart being the key definition for this point)