Now, you know that you have an ample supply of #10 envelopes (9.5" x 4"). Why not make a long/skinny card for them. It's super easy. I cut a sheet of card stock down to 8"x 7" and scored to make an 8"x 3.5" card. The flowers is a conjoined strip - QuicKutz 12" long cookie cutter Flowers border die (That I don't think is available anymore). I added some different colors of scrap designer papers to the centers and die-cut again. I then glued the colors to the extra white center circles and popped up. The black polka dot panel is 8"x 2.5". The card took 10 minutes to make and two days to photograph.
Please come and show us how you are inspired with your creation.