Log4Net and extra fields

Is it possible to insert extra fields into the database and use them in log4net? I have a UserId I would like to have in an extra field in the log-table.

I have added the field in the log4net.config:

<parameter>
    <parameterName value="@userid" />
    <dbType value="guid" />
    <layout type="log4net.Layout.RawPropertyLayout" />
</parameter>

But how do I update the ILog interface to support the extra database field. So I could for example log:

 log4net.LogManager.GetLogger("logname").Fatal(message, exception, userid);