The only way to do it is to add a 'user defined symbol', line when making a break in a dimension line (not that I ever break dimension lines...).
On the menu select 'insert > symbol > user defined...'. In the dialogue that appears, select 'utility directory' from the 'use symbol in:' drop down menu, then in the right hand list of options, select 'gap 25'. In the middle of the dialogue, one can choose the 'define symbol size by' options. Select 'length and height' from the drop down menu, then change the length and height to a size such as 5 x 5 (this make a invisible rectangle, which will be used as your break). Now, in this order, choose the icon to the left of the four icons near the bottom (add to drafting object), now select the dimension you would like to add a break/gap to (anywhere on the dimension is fine), then press again on the same dimension where you would like to place the break (the cursor location as default will be the lower left corner of your 5 x 5 rectangle). This can be used to trim arrow lengths etc.
I know it's a long process, but it's the only way I have found to do this... (any other suggestions would be most appreciated).