php date_format()ante-和post-meridian with periods

I am wondering if it is possible to use PHP's date_format() to specify the abbreviation for ante-meridian and post-meridian with periods.

For instance, the manual indicates these codes:

a   Lowercase Ante meridiem and Post meridiem   am or pm
A   Uppercase Ante meridiem and Post meridiem   AM or PM

However, our organization's style guide calls for a periods in the abbreviation, like so:

10:00 p.m.

We are using the Drupal CMS platform. It has special date-formatter tools for its fields, which allows one to specify a pattern that date_format() will accept. So, in this situation I am not easily able to add some php code to look at the abbreviation and add periods appropriately. To avoid a large work-around, I must simply specificy a format string for the date_format() function.

Is there a way I can get the date_format() function to return an abbreviated am or pm with periods?