Strategies I have seen work:
1) On every unit have a nurse who really wants work full time but tell her you can only give 75% hours for now and will build up but you will consider her for every call out so that hopefully she will end up with 100% hours..... I am not endorsing this, just passing on an idea that I see works successfully
2) If there is too many call outs on one unit, call a meeting explain that because of the call-out problem you will have to hire another nurse who will have to be given an equal slice of the pie so that there will be less for everyone, you wish you didnt have to do this, but your responsibilities lie with consistent patient care and if the present staff cant cover their units shift responsibilities, you have to bring in more staffing. Unfortunately seniority wont mean better shifts, everyone will be given fair shares of hours - even the new staff. (it goes without saying that staff that dont welcome new staff will be dealt with on an individual basis).
3) Overtime is usually according to whatever is the norm in the state/region (according to location), Find out what other facilities or hospitals in your area are paying for overtime.
4) Often we allow the nurse who is forced to work an extra shift to take off a future shift and ask the call-out nurse to take it. This doesnt always work but is an option.
5) We have sometimes called back the call-out nurse and said, we called everyone and no one is available, you will have to come in anyway (unless she is sick herself) and find someone else to (watch your dtr, stay with Mom at the hospital, or whatever) However we can give you tomorrow off and "Betsy" can cover if that helps.... OR if the call out is because of an unexpected funeral or event, we will find a way to give her two hours to attend and return, and find someone who is close by and can cover for the two hours, of course we do full shift handover with each coming and going of nurse, we dont like it but in an emergency situation we allow it, and it goes without saying that no one gives meds that someone else prepared.
6) Every so often I will ask a nurse from one unit to cover another unit just so she be familiar with the unit, in case of call-out she can cover the unit and it wont be foreign to her. Also if there is a unit nurse on vacation, the nurse from another unit who is now familiar with two units can help cover during her unit nurses vacation.
This is not a new problem, it is great that we share ideas on this, Anyone with other ideas, Please share!