How to pre fill a custom field with type select over an URL

Juergen Krieger

I already found: https://confluence.atlassian.com/jirakb/creating-issues-via-direct-html-links-159474.html

resulting in: /secure/CreateIssue.jspa?pid=11401&issuetype=10504&customfield_17002=product1

And know how to prefill project, issuetype, jira fields. ....

Also custom fields work.

But how to pre select the value/option of a custom field select field 

&customfield_17002=product1
OR
&customfield_17002=20907

does not do the trick.