Honeymoon Donation Box?

Me and my boyfriend are on a big budget with our wedding. We started talking one night about affording the honeymoon and he said, "Can you have like a box next to the gift table that says, "Honeymoon Donations" and maybe make a note like, small donations only. We starting comtemplating, is that tacky...or acceptable? would it be frowned upon? I think if I saw that at a wedding, I'd still put $5 in or something...it wouldnt be a big deal to me, like "how dare they ask for more gifts!!!!" but would anyone have that reaction? Be honest...I'm not on either side of this debate yet...It was just an intriguing question that popped up.