The free agent idea holds the most weight, but even then few teams will offer more to Euro players than the Euro leagues themselves. A separate Euro-draft, in the form of the NFL's supplemental draft, could work, but I don't really see any major flaws right now; if guys like Splitter and Vasquez don't want to play here, then that's fine. The NBA will be okay without them. However, if they want to collect the maximum paycheck, they'll find their way to the states and establish themselves as NBA stars. While the Euro clubs can currently compete with the mid-level exception and rookie pay scale, that's their upper limit, which gives the NBA a distinct advantage.
While it's sad to see Euro guys come over for a few years only to go back to Europe/Asia, it's no big loss to the NBA. If these players are good enough, they know where their big paycheck will come from, but they aren't going to get it without proving that they can play in the NBA first. While these other leagues are gaining more power, they aren't necessarily draining it from the NBA.