"Glorified rowboat", eh? That gives me a really neat idea.
Here''s what you should do: Buy a couple of oars and rig the boat so that you can use them as the mast and boom.
I''ve got the details already worked out for you. Buy 10 foot oars, drill a hole in the end of the handle of one oar. Use this handle as the base of your mast, you can step it on the floor of the boat on a strong pin (like a pintle for a transom hung rudder)sticking up to receive the hole you drilled in the end of your "mast". Install a stout board passing athwart the gunnels to slide the mast through. Drill a small hole for a cotter pin in the oar shaft just below the bottom surface of the crossboard to keep the mast from lifting off the pin. This arrangement will allow the mast to rotate with the wind, wrap some leather around the oar where it passes through the crossboard (or put a teflon sleeve in the hole in the crossboard). Install one of those "landlubber" oarlocks, the kind that encircles the oar and clamps to it and has a swivel pin that goes in the oarlock plate mounted on the gunwale. This oarlock should be above the crossboard, it will be your gooseneck fitting. Drill another hole in the end of your other oar, this will receive the swivel pin ("gooseneck") on the oarlock on your mast. If the crossboard is installed at the right height relative to the mast base pin (say half the boat''s beam minus 6 inches), the oarlock "gooseneck" will be in the right position for rowing without having to reposition it.
Now make yourself a custom sail that will slide over the end of the oar, just a sewn-in pocket like a laser sail. You should be able to make it at least 8 feet high, or higher if you''re willing to try longer (12 foot) oars. The foot of the sail can be shorter than 8 feet, or just as long or longer (depending on how far forward you step the mast), you can even give the sail "roach" by adding battens (though you''ll need to do more sewing to beef up the batten pocket ends so that you can tension them a little). This could yield you sail area of from 35-50 square feet, which is about half to two thirds a Sunfish''s sail area. Then rig a simple outhaul on the clew, maybe by attaching a metal ring to the clew with webbing, attach a small strong line to a bullseye or some other fitting on the oar, back through the clew ring again, then tie to a cleat for a 2:1 purchase. You can also rig a simple downhaul for the sail. You''ll also need a rudimentary sheet, probably a simple rope traveler at the stern of the boat and a simple block and tackle sheet attached below the outhaul fitting on the "boom" oar. You can also attach a boom vang to the second oarlock swivel attached to the boom to keep the boom down on a reach if you want to get really fancy.
You will then be the toast of the lake, having a dual propulsion system at your disposal, ready for conversion on the fly. Set the sail when the breeze is up. When the wind dies, you will be able to paddle home in style. If the wind blows so strongly that your unstayed "oar" mast snaps, you will know that you should have stayed home. Hopefully you were smart enough to bring an extra oar. Maybe the third oar could be used as a tiller, too. In that case, you will have to name the boat -