You can't with a summary field, but you may be able to set this up with a calculation field that computes the same results. A Sum function can give you the total of a specified field from a group of related records--the trick is to set up the relationship to match to the records you want to summarize.
Can you elaborate on your remark? I am interested in using a sum function to add together every record in the table that has a certain foreign key. Running into troubles and wonderinf if you had some helpful hints. Thanks!