Seven card stud odds shortcuts

Are there shortcuts similar to the rule of 2 and 4 in Texas Hold'em, for calculating odds in the seven card stud poker variations?

I suspect that due to the fact that there are no community cards makes it difficult to come up with simple shortcuts like in Texas Hold'em. However, after running some quick calculations for heads-up and 3-way play, I did come up with some numbers.

For heads-up play, there are 44 unseen cards after 5th street, and 42 cards after 6th street. Multiplying the number of outs by 2.27 will give the probability for making the hand on the river (7th street). Multiplying the number of outs by 4.65 will give the probability for making the hand on the turn (6th street) or river. So the rule of 2 and 4 are fairly close.

For 3-way play, where all players stay in the hand to 7th street, there are 41 unseen cards after 5th street, and 38 after 6th street. The numbers change to 2.4 for the turn and 5.1 for the river. In this case, it could be called the rule of 2 and 5.

With more players in the game, and the likelihood of many of them folding, the number of unknown cards will vary from hand to hand, so that odds calculations will have to be done on the fly.