There are multiple angles in the DH debate. So-called baseball purists claim that any change to the game makes it somehow less spectacular than it's original, unaltered state (as if it's still anywhere close to the same game played in the 1860's). By and large, fans of American League teams seem to support a unilateral DH rule, as it wouldn't really affect their teams except when they play in NL parks, and it would only impact them positively anyway. Many NL team fans cite their love of the advanced late-game strategy that the lack of a DH demands; managers must weigh the pros of a pinch hitter against the cons of removing a starting pitcher who is performing well. Some people want their to be a universal rule either way, by either removing the AL DH or implementing the rule in the NL.
I think there is a way to satisfy everyone's joneses.
The rule would be the same for both leagues, and implemented at the same time, at the start of a season (obviously spring training would be the time to work out the kinks).
At the start of every game, one player from each team shall be named as the Designated Hitter (DH). The DH is eligible to be placed in any spot in the order at the presentation of lineups. The DH will hit for one defensive player, called the Designated Fielder (DF), who shall also be named at the presentation of the lineups. The DH will take the turn at bat of the DF every time his spot in the line up comes up, UNTIL such time that the DF is removed from the game for any reason. From that point forward, whatever player replaces the DF in the field shall take the next turn at bat for that spot in the order, and the DH becomes ineligible for the rest of the game. Alternately, if the manager knows they are going to be lifting the pitcher soon, they can move the DH into the field, forcing the pitcher to now be considered a batter, as is currently the rule.
Example: Chicago White Sox designate Jose Abreu as the DH, and he will be hitting third for starting pitcher Jose Quintana, who is the DF. After LF Melky Cabrera, batting second, makes the last out in the bottom of the 5th, Abreu is due up in the bottom of the 6th, but in the TOP of the 6th, Quintana runs into trouble. The manager now faces the dilemma of losing Abreu's bat in favor of getting Quintana out of the game before he gives up too many hits. The manager elects to replace Quintana with a relief pitcher, Matt Albers. In a straight substitution scenario, Albers would now take not only Quintana's place on the mound, but Abreu's third spot in the lineup as well, batting next in the upcoming inning. Alternately, the manager may wish to employ a double switch, putting Leury Garcia in LF, batting in the third spot, and putting Albers into the 2nd spot in the lineup, which is now vacated by Melky Cabrera. Or, if the manager knows he is going to replace Quintana, he can move Abreu to 1B, at which point starting 1B Adam LaRoche, who was batting fifth, becomes ineligible, and Quintana is now considered the fifth hitter.
You get the AL offensive prowess of a DH as long as the starting pitcher is doing well, but once you take him out, the NL style strategy takes over. You can, with creative use of substitutions, keep pitchers from ever coming to bat in many games, at the risk of emptying your bench, but it still requires a keen strategic mind not only in substitutions, but in creating your lineup as well (if your DH is likely to be replaced by a pitcher (or utility player in a double switch) at some point, are you really going to bat him fourth every game?). It would also discourage managers from using their most potent bat as a DH on a regular basis, in that the DH will likely be pulled after two at bats.