Update ETA of one bar with ETA of the other?

[KomradFluP]

I have a script that runs other scripts in order. I've made a multibar instance and on that a singlebar that shows the progress of all scripts.
I.e. 50% 3/4 Now running: refactorTest.
I pass the multibar instance to all of the scripts so that they can make script specific singlebars.
However the problem I have is that my main bar will show 3s because the first script took that long, but the bar of the currently running script will have 30s for example. Is there a way to update my main bar ETA with the currently running script's bar?

[AndiDittrich]

just create a simple wrapper and implement your own eta calculation. values can be displayed via custom payloads