Ok, being a fan of volunteering and recipient of various financial aid myself because of it, I have some things I can say that might help you.

1. Sometimes you can participate in many activities  but I suggest creating a list on MS Word of only the activities/ groups he has been involved in that shows how he contributed and  what was learned . Sometimes its a plus if it was a position that taught him valuable skills.

Ex:  say he wants to major in visual arts. He volunteered time being a custodian in campus events. Now one might say, how can I use this when it is not related to my field?----this is where I say you dont neccessarily have to put positions you held relating to your major- but again its what you learned from it- team player, establishing and maintaining sanitary regulations,etc.---its almost like doin a resume. Use your words.

2. As for the hours- by focusing on the volunteer experiences that he was active in for awhile, you should be able to write down an clear estimate.  Usually they want to know hours and length of time. Say if it was within a schoolyear,maybe you didnt participate in it every month but  list it ( i.e.August 2004- May 2005) Calculate  hours in your typical Meetings a month ( maybe each lasting 2 hours each), Activities- maybe you cant remember exact hours but you know how many activities are usually done monthly- use that estimation .

Remember it does not have to be completely exact hours- but an estimate. What they will focus on is what was learned, what you contributed.

3. Also another thing is having much volunteer experience is great but dont overexaggerate because one may wonder how you have time for your academics with all your 'volunteering'. Thats why I say only list the key positions ( ones that show accomplishment, made him a better person, ones with the most time spent). That should help you remember some activities easier.

If you are still unsure about what to put or words to use , you could always email me questions. Hope this helps.