Can't give you a definitive answer for Prestwick but it's quite common for ILSs in the UK (don't know how common it is elsewhere) to have range info provided by DME rather than markers - this all originated before GPS, of course. For runways with an ILS at both ends it's achieved by putting the DME at the mid-point of the runway any setting it up to read zero at both ends. In the early days of FMSs this caused minor problems because aircraft equipment assumed that all DMEs said zero at their location - but I gather this issue is now covered by the navaid databases.
Don't know for sure nut I would expect the missed approach to be designed around what the DME reads - whether a new-fangled RNAV thing or a raw data display like I used to use.