First, they must be doing this service representing the bank, not as a personal activity.
Second, typically fundraising is done as part of a board member service for the nonprofit. If that is your case, then write up the board service, which includes fundraising.
If your bank's employees are not doing this as part of a board service, then you need to document how these employees were representing the bank and include specifics on how they fundraised, how much was raised, how they used their employment status to raise funds and that as bank employees, they were able to raise substantial amounts....something like that. Include the number of hours and away you go.....
Societies that do not find work in and of itself "pleasing to God and requisite to Man," tend to be highly corrupt.