Um, why would you need to? If you're holding at a waypoint in your active flight plan, hitting the OBS button before reaching the waypoint will temporarily disable automatic waypoint sequencing and then you can use the CDI for holding. I dont' think it'll diagram a hold out of the blue.
The best you can do without plotting the actual hold on the moving map display, in my opinion, is if you have dual 430s (I'm sorry, I'm a spoiled Riddle brat
). What I like to do is have the top and bottom crossfilled (both having the same active waypoint), and then prior to reaching the fix, pushing OBS on both units. As aloft said, this disables the unit's automatic waypoint sequencing. What I do is have the top unit on the first NAV page, which shows information such as BRG, DTK, TRK, ETE, etc. On the bottom, I'll have the moving map.
Now, to clarify, the top 430 shows data on the HSI, while the bottom unit shows data on Nav 2. With OBS activated on both units, I can use my HSI for the actual hold, but then twist in the inbound heading on Nav 2. Since the bottom 430 is in moving map display, I get a nice magenta line showing the radial I want to stay on. And since the top 430 is on the first NAV page, I have all the information I'll ever need. Pretty spiffy.