In the portfolio manager you can open under “Graphs” the portfolio/components/ tree. Here you can set a multiplier for leverage. This way you can for example use TLT with a multiplier of slightly less than 3 to replace TMF.
Trading cost should work, but you need to enable it with the check box in the “settings” window. Here you can set default trading costs, which then apply to all ETFs. If you enter trading costs in the symbol window for an individual ETF, then these will replace the default trading costs.