If you prefer to suggest that your community donate to a cause in lieu of sending sympathy flowers, you can update your loved one's memorial website with information on how to donate.
Start by clicking on 'Edit memorial' while signed-in to your account.
From there, scroll to the bottom of the page where you'll see a section called 'Expressions of sympathy.' In this section, just select 'Donation to a cause' and fill out the name of the cause, a brief description (e.g. "Please consider donating to the American Cancer Society in Edward's name."), and the website of the cause for people to donate on.
Once you've clicked "Update Website" to save your changes, you can see the new donation section added to your memorial's pages, like so: