If I cared enough to do the work, I might use a basket of currencies, like special drawing rights.

As of August 2023, the XDR basket consists of the following five currencies: U.S. Dollar 43.38%, Euro 29.31%, Chinese Yuan 12.28%, Japanese Yen 7.59%, British pound sterling 7.44%

It would take a little extra math to exclude the USD allocation from the basket.