Proper dryer venting is as or more important than many other things you can do that seem dangerous in the home. For instance, if you use rigid 4" venting, and you install screws to hold it together, you are creating a fire hazard. The screws catch lint like a bad artery catches cholesterol, and fire can result.
Additionally, there are codes for dryer venting. I am no expert, but in general, a dryer should never be vented more than 14' in a straight run, and 2' should be deducted from that amount for every 90' bend.
These are general guidelines. Getting the dryer vent as short as possible will also improve the efficiency of your dryer, and reduce dry times. I would recommend consulting with a mechanical contractor in your area, or an appliance dealer. The furnace installer should have given you a better course of action.
Whatever you do, don't install any plastic flex venting.