This is one of the few things I find frustrating about Sibelius (after two years of experience). Finale has several "points of articulation" which can be dragged to create the appropriate slur shape, whereas Sibelius only allows one to alter the endpoints and the curve in general.
While Sibelius does allow one to shift the "point" of the curve along the line, it's essentially impossible to slur a passage with large jumps and make it not look awkward. The slur must take on gigantic proportions, placing the crest of the curve well above the notes themselves and wasting vertical space between staves. (I have been unable to do this with multiarc slurs.)
I see that Sibelius 5 still perpetuates this problem...