I'd suggest that exchanging promissory notes based on silver, or anything else one might take in exchange for something, would be sufficient for what you guys are discussing. I try to encourage people to consider every transaction a trade. "Purchasing", exclusive of exchanging, is a myth. I assume it's a tool to allow us "spenders" to be measured, and taxed.
Anyone could write a promissory note, or a check, for an amount of silver, in exchange for some sort of services, or an IOU, gift certificate, etc., for the negotiated services. I can't remember all the factors that are necessary for the note to stand on it's own (legally, if that is a concern), but Lex Berezhny covered some of them. As well as a payor, payee, a date, a signature, and the amount of whatever negotiated needs to be listed... as well as something else I'm sure I'm forgetting. These can be endorsed, and exchanged. If they ever got back to the originators hands, s/he could destroy it, or simply exchange it again instead of creating a new one.
Exchanging IOUs, or promissory notes payable with silver, could be negotiated between parties for any service, or hours of labor, and I think it would suffice for what it is you guys are discussing with the Shire Hours concept. Like one of you already pointed out, you might be willing to promise an hour of yard work before you'd be willing to promise 10 minutes of plumbing work, or vice versa.
I found the eLiberty Dollar service to be very useful, while it lasted. I'm not entirely sure what Shire Silver will become, but I'd love to see that type of service available again.