How can you simulate the pancakeswap transfer and get the output values

I'm trying to simulate a call the transfer / transferFrom function from a certain contract without submitting it to the blockchain.

This function is used by some contracts to implement some sort of taxing system before any buy/sell.

An example of some tax implementation would be:

function transfer(address recipient, uint256 amount) public override returns (bool) {
    amount = amount.mul(0.8); // tax 20%
    _transfer(_msgSender(), recipient, amount);
    return true;
}

The leading _transfer call is then altering the internal _balances variable with the modified amount variable.

Straight of the bat, I do not want to change the state of anything as that destroys the purpose of the simulation I'm trying to achieve.

This means that I have to use address.staticcall to call this function, since it does not alter the original state. (at least that's what I think it does, correct me if I'm wrong).

The issue now is that the transfer function does not return the modified amount variable. It only returns true or false, and this is pretty much where I get stuck.

How could I retrieve the modified amount variable? Do I need to use assembly or is there some other way of achieving this?