How to make a charitable donation as a wedding favour

You can put the lump some and write on behalf of the wedding guest of Mr. & Mrs. Depending on the amount you put, only the company will know who it's from. You can then advise your guest that this amount of money was donated to this charity instead of favors.

If it's a huge amount like a million dollars is when they will place a plaque in your honor.

I'm of the opinion that your act of donating should be kept to yourself. For one thing, a wedding favour is meant to be a gift to your guests for attending the wedding. Your donation does nothing for your guests. Another is that wedding favours are becoming less traditional and it's perfectly normal to not give them out at a wedding, so no one would think twice about it. Announcing to your guests that you're donating to charity in lieu of you giving them favours can come off as you patting yourself on the back, or you asking for acknowledgement on being charitable.

I also would highly recommend against sending the charity the names or any contact information of your guests. Notwithstanding how people may feel about your chosen charity, you shouldn't be divulging other people's identity information to a third-party organization without their permission.