Practicing that one lick (or several) in a piece that you just can't play well is a daunting task. Its more
than that, its frustrating. But, without this frustration, how do you expect to learn? Being frustrated is an opportunity to steadily workout any playing issues and learn using a game plan.
One of the many tools you can use in practicing (and performing) is note grouping. It's self explanatory, you simply group notes together, looking for patterns that may help, even speed up, the learning process. By doing this, you begin to see the figure differently. Some combinations are often more difficult than what is written, which is another good way to work things out. By practicing note grouping slowly, it will often result in better fluidity (mental, finger dexterity, musical flow, etc.).
A great book to help understand this, is Note Grouping by James Morgan Thurmond.
Some other things you may consider, along these same principals, is varying your dynamics (playing the opposite as what is written or playing more than what is written), and changing the rhythms. I would say that changing the rhythm is one of my favorite ways of practicing - and, it is much more aligned with the ideas of the above book.
I encourage all of you to be extra-adventurous and creative in your practicing. And on those really difficult licks, give note grouping a try.