For example, the user might select the fields she wants to see rendered in jqGRID from a drop down menu, say "Field_1" and "Field_2".

so this would be used to construct the following:

var urlString = 'server.php?user_fields="Field_1,Field_2"'

then the url parameter for jqGRID could be set to

url: urlString

Is the idea above even feasible to try to implement?

Is there a full example?