Chess.com variants has the ability to create custom board dimensions like 10x8 but currently it doesn't have any piece that can summon another piece. I don't think other apps like Chesscraft could do too but I could be wrong.
The only way you could allow summoning of pieces is with Crazyhouse option.
I want to create a 10 x 8 board with a new piece next to each tower that has the power to summon pawns on the next diagonal square (or on the next square ahead), but can only move once to the side. I wanted the site to have a structure for creating pieces