Is there an option in wealthlab to force the yahoo data to adjusted when there is a split? Have you checked the documentation or the website to see if the program can automatically adjust the data on splits?
If not their would be a couple of ways for you to do it. One would be to find a program that downloads yahoo data and saves it as a CSV file. Another way is to write your own chartscript to create CSV files with the correct data. Wealthlab can use CSV files as a data source.