Ummm...is there a particular reason why you have to use binary variables? You can do something like this with regex to get the string you want:
Code:
on *:sockread:creds.*: {
  var %data
  sockread %data
  if ($regex(%data,/BinarySecurityToken Id="PPToken1">t=(.+)</wsse:BinarySecurityToken>/)) {
then use $regml(1) to reference to the string.