FT,
That is possible on some jets - I used to fly a glass Boeing which gave you the option of holding at present position. No knowlegde regarding the Airbus. On ours (a Classic, no Nav screen but with a reasonable FMC) you can hold at any point simply by telling it to. If there isn't a defined waypoint, you can create one up, enter and execute it and then create a hold. Not instant, but pretty quick all the same.
As I mentioned, we don't have a Nav display and when we tune the ILS (our NAV controllers can either have the ILS or VOR but not both) we lose a lot of our position information now the NDB has been de-commisioned. Therefore we tend to slow up earlier to prevent being caught out. The times we arrive (freight), we don't tend to get the guided tours so we are happy the way things are.
We are getting a NAV screen soon, courtesy of the european RNP requirements so things should be better.