If any . . . (conditional move saves)

How hard is it to program an "if any, then" conditional move option?

It's a dangerous option if the mover is careless. Sometimes it's just the best choice and it saves time.

Great idea.
I was reading a book about the "Modern Defense" where black plays 1...g6 and 2...Bg7 against everything and how an enthusiastic correspondence chess player received a game in the mail.
1.d4
Black who loved the Modern played 1...g6 and wrote..."any move...2...Bg7"
White replied...
1.d4...g6
2.Bh6...Bg7?
3.Bxg7!
Black resigned.

@chessturd said
Great idea.
I was reading a book about the "Modern Defense" where black plays 1...g6 and 2...Bg7 against everything and how an enthusiastic correspondence chess player received a game in the mail.
1.d4
Black who loved the Modern played 1...g6 and wrote..."any move...2...Bg7"
White replied...
1.d4...g6
2.Bh6...Bg7?
3.Bxg7!
Black resigned.

@chessturd said
Great idea.
I was reading a book about the "Modern Defense" where black plays 1...g6 and 2...Bg7 against everything and how an enthusiastic correspondence chess player received a game in the mail.
1.d4
Black who loved the Modern played 1...g6 and wrote..."any move...2...Bg7"
White replied...
1.d4...g6
2.Bh6...Bg7?
3.Bxg7!
Black resigned.

He probably knows the book or even owns it. I can't remember the title considering almost all books on the Modern Defense are called exactly that.
I don't think Greenpawn looks in this forum.