save string / storing readkeys WORD in a variable

In an experiment i want to use several sequential responses using readkeys. I can assign the numerical responses to separate variables for later saving. However, PsyToolkit can only work with whole numbers as values for variables, so the approach below results in NaN for the RESPONSE1 and RESPONSE2 variables. How do I save the WORD for several responses? Ideally I'd like to have just a single line per trial in the data file, so I'd rather not call save on each response collection. Since save WORD works if called directly from readkeys, it must be able to deal with string variables. Is there any way to store a string in a variable for later use (maybe by computing a numerical representation of it)?

part collectResponse1
  readkeys @18 &MaxResponseTime
  set &STATUS1 expression STATUS
  set &RESPONSE1 expression WORD
  set &RT1 expression RT

part collectResponse2
readkeys @18 &MaxResponseTime
set &STATUS2 expression STATUS
set &RESPONSE2 expression WORD
set &RT2 expression RT

task rsvp
  ### some code deleted here
  set $T2PRESENT @20
  save $T2PRESENT &RESPONSE1 &STATUS1 &RT1 &RESPONSE2 &STATUS2 &RT2