Not sure how do-able this would be. Or as well, how much of a mess it would likely make. Could you not make every reasonable attempt to seal the spoke holes (air tight) from the inside the next time you have the tire off. Then drill the rim like you were going to install a rim-lock only put in place a schrader valve. When you re-install the tire, the tube of course would be 'filled' with sealant. Before the tire bead is pryed back onto the rim, dump some sealant in to flow between the tube and rim. My thought is this would further seal the spoke nipples and tire bead. Should the tube loose air, some would still be held within the tire casing. With a compromized tube, air could still be added to the tire casing via the secondary schader valve in the rim. Just a thought. Gerry