Answer:

For example, if you want to run your cron job script every 30 seconds, you can follow the below steps:

1) create a "agent" php script with following code:

<?php
sleep($_GET['delay_seconds']);
echo shell_exec("wget YOUR_CRON_JOB_URL");
// or if you want to execute a command in your server, use the following line of code instead of above line:
// echo shell_exec("LINUX_COMMAND");
?>
2) Place this agent php on your webserver, and add 2 cron jobs (that run every minute) on easycron:
http://your_agent_php_script_url?delay_seconds=0
http://your_agent_php_script_url?delay_seconds=30

The above workaround should achieve the same effect of running your cron job every 30 seconds.