Hey Jimbo.... I had a similar problem and used an x-acto knife (kind thats used in hobbies like model plane building) they are very sharp. Try scraping using an x-acto knife as close as possible to the base, that'll knock off 99% of the shroom, then just scrape the rock a bit more to get any left overs off.
I'd gladly go pick up any shrooms you cut off.
If you ULTIMATELY pull the rock, I could trade you a rock to replace that one.