How do I take the splash out of culture bombs?

[Unit Needs Orders]

I've been mucking around and one of the things I put in was buildable "great artists" who cannot trigger a GA or build the culture tile improvement, just culture bomb. The idea is that civs can spend hammers/gold to expand their land but not instantly, and with the possiblilty of being stopped if the player is sloppy.

However, I only want it to affect the tile the artist is standing on, otherwise it's a bit much: even with a 1 tile radius it's way too powerful for a buildable unit. Setting the radius to 0 turns the ability off, unfortunately. If there are any ideas to get around this, or if someone already has a solution and I missed it, answers would be very much appreciated!

[Procylon]

I don't think there is. How about increasing the cost by 500%?