Yes, there is a way. Suppose the PHP program is located at:
http://localdomain/crontask.php
In your Crontab, invoke this command:
(if you have wget)
wget -Q http://localdomain/crontask.php
NOTE: I don't know what the flag for "quiet mode" is. Do "man wget" to find out.
(if you have curl)
curl -q http://localdomain/crontask.php
NOTE: once again, I don't know what flag is for "quiet mode". Use man to find out.
(if you have lynx)
lynx --quiet http://localdomain/crontask.php
NOTE: lynx is different. There are a couple more flags you need to add so that lynx runs without generating output.
So basically the CRON will visit this PHP page on every time interval. As a result, the PHP program will do what its supposed to.
If you have trouble finding out the exact flags for wget, curl or lynx, post another message and I'll find out for you.
hope this helps!
-sridhar