Here's a thought. The WRU often offer rewards for when Welsh players do well in competitions. For example, in 2009-2010 each player would gain £28000 and £65000 for AI and 6N sweeps respectively:
here. But I don't see why there should be a monetary incentive to do well - the desire to win should be strong enough. Instead, I'd like to see reward money much reduced, and it just given to players. Something like a £65000 reward for a grand slam reduced to £20000 with the £45000 just given out for appearances - £9000+ per appearance. There are more than 10 Welsh games a season, so this would add up to £90000+ per year, which would offset a lot of the money that French teams would offer. Then the WRU only has to operate a "play in Wales to play for Wales" policy.
If you work it all out - say £10000 for a full-appearance, £7000 for a part-appearance, £3000 for being in the Welsh squad but not playing. That's £242,000 per game for a 35-man squad. Saying there's 12 games a season (5 6N games, 3 summers, 4 AIs), that's a £2.9m bill a year for the WRU. A lot of money, but certainly manageable for the WRU. But they could also operate a policy where appearance money is limited to the first 10 games of each year and I think that would work as well. Players like Mike Phillips can expect to get around £100K from Welsh appearances then, plus more if the Welsh team achieve things. I think that this would offset the French-pull.
Just a question of whether the matter is worth £2.5-3m to the WRU.