civicrm/payment/ipn url in wordpress does not handle & (for some processors)

An ongoing issue with payment processors has been that they often do odd things with the return url - in general having & or ? signs in the return url can be problematic as they can be unpredictable.

In drupal the civicrm/payment/ipn/xx url works pretty well on all processors as long as clean urls are enabled, which is pretty standard.

I am currently looking at Payment Express on wordpress - the return url as they encode it is

wp-admin/admin.php?page=CiviCRM&q=civicrm/payment/ipn/4&&result=0000030044018882001ee45fac197dff&userid=Fuzion_Dev

Note they encode OUR & but not theirs in that url. The problematic part is this

&q

instead of

'q' => 'civicrm/payment/ipn/4'

it presents as

'amp;q' = 'civicrm/payment/ipn/4'

I think we need special handling for this instance