Mels is really a one way trail starting from the Water Main Trail to the Trans Canada, having said that you can opt to hop off you bike and walk up it part way and ride most of it backwards to Gear Jammer or onto Nicoles.

You could ride up Gaglardi to the Water Main Trail (and push up that) to Mels, a good warm up and fairly fast.

Or as you did  ride up the Trans Canada to Cardiac (and push up that) and ride along the ring road (Univ. Dr. to the New Gear Jammer and then down Mels), or up and over and thru Naheeno park (by the SFU Community Garden, fast, flowing XC type single track and great if your just learning, just veer to the right and you will usually end up at Univ. Dr. just opposite the start of Mels off Univ. Dr. — just watch the ditch coming down the slope, it can be overgrown with grass and a bit of a surprise drop.

There is apparently a walking trail that does intersect Mels (?) from the Powerline trail, but you might have to ask the walkers commuting down from the Univ. about this short cut, it is not on the bike trail map.

As to what is possible that depends on your legs and your bike, my freeride/DJ bike weighs a ton and half and riding up is a tough (why you see all the heavy bikes on the bus racks), my XC bike is lot lighter and most things would be ride-able if my legs could take it (I've yet to make it up Cardiac, but have been passed by some young buck doing repeats on that hill), maybe easier with a full suspension bike too. Okay and you would probably have to walk up the steep part of the Water Main Trail, but it does have those Eagles so getting to Mels and taking a breather usually means staring up at a pair of circling Eagles, which is pretty cool unto itself.

Hope this helps.

Heading along Mels from the TransCanada entrance is definitely an option.  It's a better workout and you will prob. need to push your bike up a lot of sections.