Yes, you should be able to pass values for any response, including responses to hidden questions, using query parameters. For example, to set the collectorID response to CAT_PEOPLE, you could use https://ee.kobotoolbox.org/single/lZr49Upg?d%5BcollectorID%5D=CAT_PEOPLE. For more details, check out the following discussion:
If this does not work for iframes for some reason, please let us know.
