Fixed lenght dimensions R5

HI! Is there some way to set fixed extlension line lenght of dimension in R5? I read the topics, that in basic R5 there is no way how to do it. This function is aviable only in R6 (also localtopic). But i am quite happy with my R5, i am not going to buy new R6 just because of this, althought this issue is quite problem during making a building construction plans… what about some extensions, add on…?-- thansk a lot.