Self clearing seems pretty straight-forward from what I've read (giving it a try on a package that's due this week).
Simply put, from what I understand all you really need to do is get the relevant information (Waybill#, Unique ID #, invoice) from the shipping company, in this case, UPS and pop down to your local CBSA office to pay duties and taxes once your package is in town. Once done have them fax off the receipt/form (B15?) stating everything has been paid to UPS and you're good to receive your package without the ridiculous fees UPS charges.
I called UPS for the information, got all I needed and then noted I wanted to self clear (lady didn't seem to like the idea and sorta floated between "you can't really do it but you sorta can"). Shouldn't have a problem as I never consented or implied I wanted to use their accounting services so anything they paid to clear it isn't my problem as I'm legally entitled to clear my own packages. I already paid the shipping fee, once I've paid duties and taxes they can't deny me my package.
One thing to note though is it should be easier if you live in the port of entry (ie Vancouver) your package is coming in from as UPS and CBSA seems to state you have to physically be there to self clear.
*Do correct me if I'm wrong anywhere in the process I listed as I'm still somewhat new to self clearing. Just really don't like being burned by UPS fees.