Hello Erik,
"The variables are the free properties of the instance, task and event objects. The JavaScript types authorized for these variables are string, number and Date"
So you cannot save other than date,number or string object in to the instance variable.
But you might try SQL activity where you save your object to json string in the advanced tab
var variableA = {label:"auto",field:"sLabel"};
//to string
instance.vars.variableA = JSON.stringify(variableA);
And then nicely put back to object in the SQL activity
<%
var variableA = JSON.parse(instance.vars.variableA);
%>
INSERT INTO <%= vars.tableName %> (<%= variableA.field %>) SELECT <%= variableA.field %> FROM XtkWorkflow where <%= variableA.field %> LIKE '%<%= variableA.label %>%'
But how you do the rest I do not know....good luck
Marcel