Bit late now, but I use Joe's Rim Strips on non tubeless rims. Kind of like a manufactured version of a cut down tube, buy the widest ones you can get, the less they are stretched the thicker they are to fill the gap between the bead and the rim. Available in presta and schrader versions, so If I was dealing with the OPs problem I'd drill the presta rim to schrader and use them. Generally now what I do with non tubeless tyres is give them a small dose of a latex sealant like Stans, enough to seal them and fix any micro porosity, ride them for a few weeks then put in the correct amount of a non latex sealant like Finish Line.