Well, ratio categories like average can easily be converted from a ratio to a counting category.
First thing, come up with a replacement value average. For example say this replacement value average is 0.269
Next take the number of At Bats a player is projected to get and multiply that number by 0.269 Next subtract this number from the projected number of hits the player is suppose to get. The number you get is the amount that player is above the replacement pool value.
Example: Adam Dunn projections.... 540 at bats, 134 hits.
540 * 0.269 = 145.26
(which means someone with 540 at bats needs to have over 145 hits to be of positive value in the average category)
Next, (rounding off)
134 - 145 = -11
Rank all players using this formula for ranking value as it pertains to batting average. You have now converted batting average from a ratio to a counting statistical category much like HRs, RBIs, RUNs and SBs.
The 0.269 varies slightly, depending on the size of the pool of players your league has. More teams and larger roster sizes increases the pool size, and lowers the number.
I learned this on another message board last year, and incorporated it and ratio to counting conversions for WHIP and ERA into my Mock Draft Software Program