Symptoms
According to the documentation, there is an option to conditionally start a workflow in K2 for SharePoint, but no option is seen in the designer.
Diagnoses
The Conditional Start functionality was only introduced in 4.7, whereas customer is still on 4.6.11.
Resolution
There was no easy way to do this prior to 4.7. In theory, you could use events within the workflow, so that after the workflow kicks off, you could check conditions, and then immediately terminate the workflow if it shouldn't keep going. Or, if you use K2 for Visual Studio, your could theoretically write code behind the start rule, that might be able to verify conditions for you.
The best solution, though, will be to upgrade to 4.7.