I do believe that there should be some Alternate Class Feature that'll allow warblade to take non-warblade discipline. Well, you know, in Dragon Magazine, but it's not really easy to dig it up... Where can I find those ACFs?
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Here's the giant list of alternate class features for all 3.5 classes. There exist no ACFs for the Book of Nine Swords classes.
The canonical solution to this problem is just to multiclass.
There exist many compelling multiclass builds and your intentions are the problem that multiclassing is intended to solve.
However, for your specific requirements, two feats exist within the book to provide for the "dabbling" that you want:
While this does not allow unlimited selection from the discipline (that's what multiclassing at the appropriate level is for) it certainly allows for cherry-picking delicious delicious maneuvers. Given that you can keep taking the bloody feats, I believe this satisfies your requirements.
I don't know if it's the same as was published in Dragon (heck, I can't find anything in my dragon indices), BUT I did find the Soldier of Shadow on the D&D wiki
Hope that helps.