How about having a client sponsored contest section where a client who wants some serious custom work done, instead of posting in the “Items Requests” forum and hoping for a nibble, sponsors a contest to design and develop to their requirements.
This idea is based on the Corporate Logo contest “Jackpot” section on www.worth1000.com where I’ve picked up a few prizes over the years.
The client can offer a cash prize of their own choosing (possibly with an FD determined minimum) and pay it (plus FlashDen fees) up front to FlashDen.
They then post detailed specs, links to all sources to be used or referenced and then a period of Q&A on a dedicated forum takes place to iron out details and remove ambiguities.
An experienced reviewer can estimate what would be a reasonable time for the contest for a particular item to run, after which time all files submitted (and accepted by FD reviewers) are posted in a special section (protected, like the current files section) for display.
Members could vote on all entries (which remain anonymous until after voting) with perhaps some minor prize awarded by FD for the top member-rated file(s) (maybe free file(s) to the value of $??) ... but the Jackpot is that the client is contractually bound to select a file from the entries, that most closely matches his requirements.
The client gets the source to that file and it’s author gets the prize money the client put up.
After the client selects his file all entries move to the normal files section for general sale (modified by their authors if necessary, to remove all client specific references) so the “losing” entrants’ time and energies are not totally wasted. The clients could be offered an “exclusive” option whereby, for an additional fee they can buy exclusive rights to the selected file and it is then not offered for sale on FD (or by the author, anywhere else)
If the best-fit file is not 100% what the client needs then the client can request further customization by FD members for a negotiated fee, with the file’s author getting first refusal, or entrants can state in the comments along with their entries how much customization they would be willing to do for free, if selected. (and of course be contractually obliged to carry it out if selected, before payout by FD)
Prize offers by clients may start out a bit low to begin with, especially due to the very low pricing of files on general sale on FD and the perception that some FD authors will work for peanuts
but I imagine, like the “Jackpot” contest on W1K , eventually “fair” prizes will be offered, as higher prizes will attract more talented authors; dozens of clients are regularly paying out prizes of hundreds of dollars for just a logo design on W1K . The Flash talent on FlashDen should eventually attract even bigger prizes.
A further revenue generating side-effect maybe that if a client’s requirement could partially be met by one or more files already for sale on FlashDen, then with each contest sponsored there may be surge in sales of suitable templates 
You could start with FlashDen sponsoring the development of a fully functioning Client Request contest section to the above specs 

.