break-down a position into smaller parts

if you have, for example, a 20K posiiton it would be very convenient if you could break that down into 4 x 5k posiitons at the same entry price. the reason is that you might want to move the position (by doubling it) quite some distance and then let the market take it out profitably. if you don't have enough margin to double the 20k position 4 or 5 times, you might have the margin to double a 5k position 4 or 5 times; have it taken out; and then do that again with the next portion of the position.