It will depend on the overall meaning of the sentence:
You only need the 2nd helping verb if the sentence is ambiguous without it.
here's an example:
james is more likely to meet with thomas than lydia
--> unacceptable, because there are two meanings.
in this case, you have to add a helping word to dispel the ambiguity:
james is more likely to meet with thomas than is lydia (meaning #1)
james is more likely to meet with thomas than with lydia (meaning #2)
james is more likely to drive to work than lydia
you don't need "is" here, since this sentence can only mean one thing. (it's not wrong to include "is" -- just not necessary.)
Giving kudos is the easiest way to thank someone
Nothing can stop the man with the right mental attitude from achieving his goal; nothing on earth can help the man with the wrong mental attitude.