Little help with post_class( ) template tag

Hi there,

I have a post_class() template tag in my index.php template that i would like to add a custom class which is generated by my admin options.

The post_class() should output like this:
<div <?php post_class( classFoo class2 );?>>

Now, classFoo is generated by my options page but i don’t know how to add it to the template tag dynamically. class2 is already in the tag.

Here’s what i got now:

This echoes the classFoo
<?php echo $smof_data['custom_class'];?>

i tried added it to post_class() like:
<div <?php post_class( 'echo $smof_data['custom_class'] class2');?>>
but obviously it doesn’t work.

Php is not my strength.
I suspect this must be a easy thing to accomplish.

Can anybody please please please help?

Cheers Alex