Hi Mariah! It sounds like you have something special in the works! For assistance, you can start by contacting
Disney Weddings - they also assist with engagements (you can find the phone number within the hyperlink). Hopefully they can point you in the right direction once you provide them details of what you have planned.
If that doesn't work out for you, you might want to email Disney at Guest Relations (guest.mail@wdw.disneyonline.com). Give them details of what you are planning and hopefully they can assist you.
If you need to speak with a cast member once you are at Magic Kingdom, you can stop in Guest Services.
Mariah, your question reminded me of a Disney Blog post from 2009 outlining the
Top 10 Proposal Ideas at Disney. I thought I'd share it with you in case it helps with your planning. Good luck and I hope this proposal is the most magical ever!