The matter was also brought up following yesterday's memorial service for Prof. Werba, and I've tried to find out some more for my ongoing Gāyatrī study. I hope it helps somehow.
The precative is most often made from aorist stems, and is thus very close to the aorist optative (lacking the s of the precative). The aorist of causatives is usually the reduplicating aorist, and the aorist optative would therefore be pracūcudét (cf. Macdonell's Vedic Grammar for Students, p. 174, §149.4). Apparently, however, no active precative form of a reduplicating aorist is attested, and I think it would be rather speculative to postulate a Vedic aorist precative pracūcudyā́s or pracūcudyā́t.
Interestingly, the precative is theoretically also made from the present stem of secondary verbs. Both Whitney (384, §1049) and Müller (1886: 113, §385, note 2) remark that in the precative active of causative verbs, the suffix ay is to be replaced by the suffix yās. Whitney, however, regards this formation "as purely fictitious" (it would be really interesting to see if a precative like this is actually attested somewhere). Anyhow, the fictitious Sanskrit precative of pracodayati would thus be pracodyāt.
In the RV, pracodáyāt is definitely a subjunctive of a causative verb. However, since classical Sanskrit doesn't have the subjunctive, many reciters of the Gāyatrī(s) must have had some difficulties in understanding this form (if they tried to); I hope I'll gain some insight in this matter in my dissertation.
Best,
Dominik Haas