I have not worked with Gammon's library, but if you can print strings w/o any problems you can always convert your sensor values into strings. You should be able to do something like:
double sensorValue = 10.8356;
String forPrinting = String(sensorValue,4);
This will create a string called forPrinting with all the data in sensorValue. The number 4 indicates how many decimals of precision to use when converting the double to a String.
As always, be cautious of Strings, as they have a lot of limitations. In this context, though, they should work fine.
Hope this helps!