There are accepted ways to increase the caloric content of formula.
However, I would prefer to have mom increase pumping (Dr. Mom's full faucet
idea) and then supplement via tube or cup, with "top milk" for higher fat
content.

From Nutrition Focus Vol.8(6) Nov Dec 1993

to make 24 kilocal/ounce milk
Liquid concentrate 13 oz with 9 oz water = 22 oz of 24 cal/oz formula
Ready to feed formula 32 oz plus 3 1/2 scoops powdered formula =33-34 oz of
24 ca/oz formula.
Powdered formula  3 scoops in bottle. fill bottle with water to 5 oz level
after adding formula powder. = 5oz of 24 cal/oz formula


The article says osmolality and renal solute load (RSL) of formula mixed
this way will not be a problem.  Concetrating the formula to 27 cal or 30
cal/oz should only be done when intake volume fails to provide adequate
nutrition for optimal growth (after a trial of 24 cal/oz) and when there
are good reasons that the formula volume cannot be increased.  It is in
part concern about excessive RSL due to restriction fluid volume that
prevents regular use of the "concentrating" method to produce formulas that
contain more than 24 cal/oz.

3 parts formula to 2 parts water sort of sounds about the same as the
liquid concentrate recipe above.  Or consult with a dietician if you are
still leary of his recipe!

I believe there are premixed 24 cal/oz in hospital nurseries, but I've
never looked in drug store.

 Sincerely, Pat in SNJ