I used a sheet of steel roofing in a wooden frame and magnets to hold/attach the envelopes in sequence. I cast vision from the front during our announcement time that we would have the Wall up in the cafe for two weeks only. Members were encouraged to take an envelope for the amount they wanted to donate. (if you took #45, a check for $45 should be included) The beauty of compounding takes 200 envelopes, if all are returned and creates $10,100. In our effort we raised $7,000.
I was clear in the promoting that this was a "special" opportunity and should only be contributed to if it was above and beyond their normal support (we've learned that when special offerings are taken, many times members just shift their giving, which isn't helpful because it creates shortages in the general and building funds).