I think that DeepSkyStacker (DSS) does not offer different merging algorithms - however, there seems to be a way to get to the result you want, anyway:
DeepSkyStacker's FAQ has the following question:
Q: My resulting image is very dark. Is it normal?
A: [...] The histogram must be stretched by adjusting the RGB levels and the luminance in the Processing Tab.
This, basically, is the same question as yours, just asked the other way around.
The Processing Tab offers very basic editing options:
[...] DeepSkyStacker only allows simple processing treatments of the resulting picture in order to quickly view the result of the stacking process. The heavy post processing should take place in another more specialized software.
However, it should suffice here. Simply switch to the
RGB Levels-tab and adjust the picture until you like its look:
The simplest way to understand how the different parameters are working is to change them and look at the resulting the luminance adjustment curve (black curve) on the histogram.