Get a sheet of acrylic to replace the side of your case. Cut a couple of holes in that and glue short lengths of acrylic tubing so that the tube directly connects room air to the input side of each fan. (You could, just as a first quick cheap experiment, try this with cardboard, duct tape and staples. Do a good job and if it shows substantial results then do the more impressive job with clear acrylic)
Some Dell computers have have plastic ducts that route room air from openings on the back of the case directly to the top of the CPU fan. You are just doing the same for your GPU fan and CPU fan.
If you wanted to really impress people you could come up with a portable room air conditioner and duct the cold dry air out of that into your GPU and CPU input ducts.
Or if you want to go steampunk you could get some sheet copper and tubing and a good sized soldering iron and make yourself some copper fins bonded onto a copper tray. You fill the copper tray with crushed ice and the fans pull air past the cold fins cooling the air before it is sucked into your case.
Watch out for condensation. Sucking water into your computer might not be a good idea, but I did once wonder for a few hours whether it would be feasible to blow a mist of fine water droplets onto the CPU heatsink where it would immediately evaporate and decrease the temperature substantially. I feel I must say I am not responsible for any damage caused by trying this, but if someone does try it and gets video showing substantial temperature drop I think you might have some youtube material there. Post to let me know.