I just did a quick search and found this info;
I'm not sure how accurate this information is. Check out the link
http://www.historyofwar.org/articles/weapons_bf_109F.html It basically says that;
3 common field mods were used with the 109F-4.
Rustatze (Field conversion kits)
R-1 MG 151/20 cannon mounted under each wing
R-5 A 300 litre drop tank mounted under the fuselage (Is this a Rustatze mod' that we have in game or was it capable of carrying it as standard?)
R-6 ETC 250 bomb rack for a 250Kg bomb
Some more digging around has to be done to validate any claims that it indeed carried a bomb. Or that the Rustatze mods were carried out in sufficient numbers.
If the 300 L drop tank we have in game refers to the R-5 Rustatze then the R-1 and R-6 may be applicable.