getSampleSizeMeans() when two groups have unequal variances

[MatsuuraKentaro]

https://www.rpact.org/vignettes/planning/rpact_continuous_examples/
The URL above says:

By default, rpact uses sample size formulas for the t-test, i.e., it assumes that the standard deviation in the two groups is equal but unknown and estimated from the data.

but I couldn't figure out how to run it when two groups have unequal variances. If possible, could you prepare an option to give the standard deviations of two groups for getSampleSizeMeans()?