I wrote a code for creating excerpts for question lists, you can change it to apply it to related questions.
in line 15, function starts. it reads question IDs from list and get's their content in one query. then adds it to question list array.
you will need to add this code to doctype() function, find list of related questions in $this->content instead of $q_list['qs'] and get excerpts and add them to array. thats all.