the Ergodex DX1 has 25 keys in the basis packet, so you would need some extra keys, that's quite expensive then.
the Frogpad has only 15 keys, so it's no use for ENTI-key++
the Half Keyboard would be a solution, but it is missing the top number-row, so it is no use for ENTI-key++ either
we will try to find a manufacturer to produce a half keyboard, that you can attach to your hand and carry around