You can just add any ETF you do not need and then rename the csv file in the data folder and in the QuantTraderUser.ini file. Then you load the csv file into excel and replace the prices wit generic prices so that you get a 7% return per year. Now you can use this ticker.
The disadvantage is that going forward this generic ETF will not be updated. You would need to do this manually within Excel. So, this is only a solution for single backtests.