My Casio from 1994 works like that. Probably most if not all of them. You are at Var1, press Var1 again, you get the fill (next remaining beats) and then you can continue in var1 or press Var2 to jump to Var2 after the Var1 fill ends.

The only way to get the Var2 fill while playing Var 1 (orr opposite) is to press the Var2 button 2 times in quick succession. That way it instantly goes to Var 2 and the second press triggers the Var2 fill, then again press Var1 to return to it after the Var2 fill ends. Drawback is that you almost always get glitches, some Vars have different instruments assigned and the rpogram changes may introduce weird effects. Also with only 2 Vars in each style, the differences of the Vars are usually big enough to be instantly noticeable. unlike Yamaha 4 vars where the change from few instruments to more is more gradual each Var.