The screenshots are I believe self explanatory. First you select the variable number with Ctrl + W then you use Ctrl + Alt + J for the "Surround With..." feature:
Next when you choose "cast" from the list and hit enter this is the result:
It would be nice if ReSharper would automatically fill in the type for the cast giving:
Without the need for the addiontal Ctrl + Shift + Space step to auto-complete it.
The .NET Aficionado