cut some wood. styrofoam. acrylic blocks... etc
i'm not skilled like that. lol i wish i was.I had a similar problem with a 6 gallon bookshelf petco/petsmart aquarium. I wrapped a piece of black electrical tape around the top of the tank to blend in with the rim. Worked perfectly.
With my 75 gallon tank I put a piece of crown moulding around the rim of the tank. Basically making the rim go down about 1 inch lower. A larger piece of trim/moulding, and the rim would have gone down further still. You can try something that. By making the rim bigger, it gives the aquarium more of a boxed-in picture frame look (some people like it, some don't) I love the way my 75 gallon turned out. You can see it in my signature. Just check out the asian themed aquarium stand.
If you are dead set on raising the hob, then yes, this is a DIY project as far as I know. I've never seen anything that is designed for raising a HOB. But honestly, like blazingwolf said earlier, grab some acrylic/plexi/wood/foam, and some silicone. My caveat to that is this: get some graphed paper, pencil, eraser, and ruler/measuring tape. Draw an idea. Not to scale or anything, just something you think will support your HOB the way you want your HOB supported. Once you have the basic idea, plan it out on the graph paper. To scale, preferably. Once it's on the graph paper, imagine tipping the hob with your hand in every direction. What do you have in place to keep it from tipping? Figure out where you'll add a little bit of support. Once the plan is finished, start cutting and gluing.
Or just deal with the lower water level until you've saved up enough for your canister filter.
Or add an extra powerhead...
Im pretty sure thats a Fluval filter, what I did to raise my Fluval C2 was I used two bottle caps off a Poland Spring bottle, one on each side. I wedged them into that crevice between the outflow and the media compartment. That way they rest on the rim instead of the filter itself.
those type filtes usually have a leveling device on the bottom. that keeps pressure on the rim. i'd say u can raise that 1/2 inch to 3/4 inch easily and everything still be fine.
i raised my aquaclear on my 10 when i had it merely by setting the bottom edge of the outflow on the rim. never so much as budged
rim was like the one in ur tank, a two level i just set it on the first lower level. stayed right where i wanted it to
Powerhead + downward-facing spraybar + ??? = Profit!