1kg of lead is like 90mL. I just measured my quite svelte TV remote at 22cm x 2cm x 5cm = 220mL. I'm sure you could easily fit 1.5 kilos of lead in there, and with a slightly thicker "A/V receiver" style remote we could easily make that 3-4kg
As an added bonus we can pack in 70% more mass in the same space