Metal Bonding Paste

Cyanoacrylate gel adhesive would work.

http://www.pcepoxy.com/our-products/paste-epoxies/pc-7.php

http://www.pcepoxy.com/our-products/our-products.php

You want something that is "thixotropic", such as:

Tra-Con Tra-Bond 2147 Thixotropic Epoxy/Polyamide ...(non-endorsement)

Or many others. Maybe non-sag to the layman.

If flow of the adhesive is your problem, try a higher viscosity product. That will be thicker and flow less while it is curing. Another possibility would be to use a thixotropic product. These have a lower viscosity while being agitated but develop a higher viscosity when the agitation is removed. Not to be used for your application but Spackling Compound is a product that is thixotropic. Another possibility is to use a catalyzed adhesive that is intentionally made to have its set time variable by increasing or decreasing the amount of catalyst.

Another possibility, dependent upon the clearances, would be to grind up some hot melt adhesive to a fine power and coat the parts to be glued with it. (initially try some of that hobby hot melt for the hobby gun). After assembly heat the tube until the hot melt glue melts and stays in the places you want it to be. Another way might be to melt some of the glue on the outside surface of the inner rod, insert it and then remelt the hot melt glue after assembly. Let it cool and you have your glued substrates.

Also contact several adhesive manufacturers and ask them if they have such a product. If they don't ask them for a referral to some one who might. They are usually very cooperative since they want the next order of something they do make. Don't stop until you have several different sample. Test the samples and try them out on your substrates.

Good Luck, Old Salt

If the adhesive you already have is suitable for long term application, then you might consider using magnets (inside and outside the tube) to hold your items in place while curing happens and then remove the external magnets and the internal braces then just fall away.

Alternatively localised coining of the tube would capture the slugs in place with ultimate strength developed by the adhesive.