There is no substitute for an angry mob if you can get one. Once someone writes a letter they are more interested, more connected, more opinionated, etc. If the original motive was a chance to win a prize the second letter will happen and it have a different motivation.
How about this, provide easy access to congressional emails to forum members then offer that interested vapers write to their representative and two senators and if they cc the email to an email address provided it will be included in a contest. Then there is the understanding that all those emails will be posted in chronological order for all to read to may be help others develop what they want to write. When X number of emails have been posted (how about 1,000) there will be judging of which emails are the best written. Probably a way could be found for forum members to do the reviewing and vote for their top favorites. Then have crowd sourced funding for prizes (I would contribute to that,) The prizes are items carried by one of the online vendors who is paid for those items with the contributed money. The vendor is notified of the winners and he fulfills the orders after being paid by the contributors then contacted via the winners' email address to provide shippiing address, etc. If US based online vendors want to offer prizes at their own expense I see know reason to turn them down. They don't pick the winners. (the prize could also be a gift certificate from a participating vendor so the winner could choose what he wants.
If the idea flops and only a few people write emails there nothing lost. If it is a smashing success there could be more rounds with more prizes. I don't see an ethical problem here because I would expect the writing to be sincere expression of interested parties and there is no chance of getting a prize with bad writting.