Sorry that my reply is late, but maybe it can be of future use.
Maybe you could read "
A Witches Bible" by Stewart and Janet Farrar to get ideas. There's a chapter about Wicca funereal rituals known as Requiem or Crossing Over. If you're worried about how your actions will be received by Christians attending the services, why not wait and do something at a different time? You can always have your own celebration at your home with his ex wife and daughter. Maybe you can make a donation in his name to a local Wiccan or Pagan group, then present his family with a certificate in a pretty frame stating what you did. How about tending plants specifically for your friend in your own garden and then allowing any of his friends and family members to pick them and bring them to his grave? If you're not comfortable with painting a Wiccan symbol on a vase or pot, you could paint the symbol on a small flat stone and tuck it discreetly into the pot.
Any thing that you with love and remembrance of your friend will do nicely.
