I think your best option is to RGB mod your 2600Jr. I carried out the mod for exactly the reasons you've listed. The RGB mod not only allows you to switch between NTSC and PAL colour pallets, effectively making your console multi region, but if you connect via RGB you'll be bypassing the NTSC colour signal which results in black and white on some TVs. Assuming you live in a European country most/all TVs have a scart connector which accepts 60Hz RGB.
I've been playing this game a lot and would love to get hold of the full version to try the two player with my brother. Is they any way to purchase a digital version similar to what champ games offer? I'd import the cart from the store, but they aren't shipping to the UK anymore.